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Logical Volume Manager Administration

Red Hat Enterprise Linux 5

LVM Administrator's Guide

Edition 1

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Abstract

This book describes the LVM logical volume manager, including information on running LVM in a clustered environment. The content of this document is specific to the LVM2 release.

Chapter 1. Introduction
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1.1. About This Guide
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This book describes the Logical Volume Manager (LVM), including information on running LVM in a clustered environment. The content of this document is specific to the LVM2 release.

1.2. Audience
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This book is intended to be used by system administrators managing systems running the Linux operating system. It requires familiarity with Red Hat Enterprise Linux 5 and GFS or GFS2 file system administration.

1.3. Software Versions
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Expand
Table 1.1. Software Versions
SoftwareDescription
Red Hat Enterprise Linux 5
refers to Red Hat Enterprise Linux 5 and higher
GFS
refers to GFS for Red Hat Enterprise Linux and higher

Chapter 2. The LVM Logical Volume Manager
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This chapter provides a summary of the features of the LVM logical volume manager that are new since the release of Red Hat Enterprise Linux 5.6. Following that, this chapter provides a high-level overview of the components of the Logical Volume Manager (LVM).

2.1. New and Changed Features
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This section lists new and changed features of the LVM logical volume manager that are included with the release of Red Hat Enterprise Linux 5.6 and later.
Red Hat Enterprise Linux 5.6 includes the following documentation and feature updates and changes.
  • In Red Hat Enterprise Linux 5.6, the lvm.conf configuration file includes a default_data_alignment parameter that allows you to set the default alignment of the start of a data area. For information on data alignment in LVM as well as information on changing the default value of default_data_alignment, see the inline documentation for the /etc/lvm/lvm.conf file, which is also documented in Appendix B, The LVM Configuration Files.
  • In the Red Hat Enterprise Linux 5.6 release, you can use the --splitmirrors argument of the lvconvert command to split off a redundant image of a mirrored logical volume to form a new logical volume. For information on using this option, see Section 5.4.1.3.3, “Splitting Off a Redundant Image of a Mirrored Logical Volume”.
  • You can now create a mirror log for a mirrored logical device that is itself mirrored by using the --mirrorlog mirrored argument of the lvcreate command when creating a mirrored logical device. For information on using this option, see Section 5.4.1.3.1, “Mirroring the Mirror Log”.
  • In the Red Hat Enterprise Linux 5.6 release, you can control metadata storage on a physical volume by using the --metadataignore option of the pvcreate command. For information on setting this value, see Appendix D, LVM Volume Group Metadata and the pvcreate man page.
  • In the Red Hat Enterprise Linux 5.6 release, you can determine the number of metadata copies at the volume group level with the --vgmetadatacopies option of the vgcreate command. For information on setting this value, see Appendix D, LVM Volume Group Metadata and the vgcreate man page.
Red Hat Enterprise Linux 5.7 includes the following documentation and feature updates and changes.
  • You can now combine RAID0 (striping) and RAID1 (mirroring) in a single logical volume. Creating a logical volume while simultaneously specifying the number of mirrors (--mirrors X) and the number of stripes (--stripes Y) results in a mirror device whose constituent devices are striped. For information on creating mirrored logical volumes, see Section 5.4.1.3, “Creating Mirrored Volumes”.
  • As of the Red Hat Enterprise Linux 5.7 release, there are two new features related to snapshots. First, in addition to the snapshot itself being invalidated when full, any mounted file systems on that snapshot device are forcibly unmounted, avoiding the inevitable file system errors upon access to the mount point. Second, you can specify the snapshot_autoextend_threshold option in the lvm.conf file. This option allows automatic extension of a snapshot whenever the remaining snapshot space drops below the threshold you set. This feature requires that there be unallocated space in the volume group.
    Information on setting snapshot_autoextend_threshold and snapshot_autoextend_percent is provided in the lvm.conf file itself. For information about the lvm.conf file, refer to Appendix B, The LVM Configuration Files.
  • When extending an LVM volume, you can now use the --alloc cling option of the lvextend command to specify the cling allocation policy. This policy will choose space on the same physical volumes as the last segment of the existing logical volume. If there is insufficient space on the physical volumes and a list of tags is defined in the lvm.conf file, LVM will check whether any of the tags are attached to the physical volumes and seek to match those physical volume tags between existing extents and new extents.
    For information on extending LVM mirrored volumes with the --alloc cling option of the lvextend command, see Section 5.4.11, “Extending a Logical Volume with the cling Allocation Policy”.
  • As of the Red Hat Enterprise Linux 5.7 release, if you need to create a consistent backup of data on a clustered logical volume you can activate the volume exclusively and then create the snapshot. For information on activating logical volumes exclusively on one node, see Section 5.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
Red Hat Enterprise Linux 5.8 includes the following documentation and feature updates and changes.
  • As of the Red Hat Enterprise Linux 5.8 release, it is possible to grow mirrored logical volumes with the lvextend command without performing a synchronization of the new mirror regions. For information on extending a mirrored logical volume, see Section 5.4.10, “Extending a Mirrored Volume”.
  • Small clarifactions have been made throughout this document.
Red Hat Enterprise Linux 5.9 and Red Hat Enterprise Linux 5.10 include the following documentation and feature updates and changes.
  • Small clarifactions have been made throughout this document.
Red Hat Enterprise Linux 5.11 includes the following documentation and feature updates and changes.
  • This manual documents the lvm tags command, which lists the currently active host tags. For information on LVM object tags, see Appendix C, LVM Object Tags.
  • As of the Red Hat Enterprise Linux 5.11 release, you no longer need to specify a major number when using the --persistent option of the lvcreate or lvchange command. This had no effect on the major number, which the kernel assigned dynamically. For information on persistent device numbers, see Section 5.4.2, “Persistent Device Numbers”.

2.2. Logical Volumes
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Volume management creates a layer of abstraction over physical storage, allowing you to create logical storage volumes. This provides much greater flexibility in a number of ways than using physical storage directly. With a logical volume, you are not restricted to physical disk sizes. In addition, the hardware storage configuration is hidden from the software so it can be resized and moved without stopping applications or unmounting file systems. This can reduce operational costs.
Logical volumes provide the following advantages over using physical storage directly:
  • Flexible capacity
    When using logical volumes, file systems can extend across multiple disks, since you can aggregate disks and partitions into a single logical volume.
  • Resizeable storage pools
    You can extend logical volumes or reduce logical volumes in size with simple software commands, without reformatting and repartitioning the underlying disk devices.
  • Online data relocation
    To deploy newer, faster, or more resilient storage subsystems, you can move data while your system is active. Data can be rearranged on disks while the disks are in use. For example, you can empty a hot-swappable disk before removing it.
  • Convenient device naming
    Logical storage volumes can be managed in user-defined groups, which you can name according to your convenience.
  • Disk striping
    You can create a logical volume that stripes data across two or more disks. This can dramatically increase throughput.
  • Mirroring volumes
    Logical volumes provide a convenient way to configure a mirror for your data.
  • Volume Snapshots
    Using logical volumes, you can take device snapshots for consistent backups or to test the effect of changes without affecting the real data.
The implementation of these features in LVM is described in the remainder of this document.

2.3. LVM Architecture Overview
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For the Red Hat Enterprise Linux 4 release, the original LVM1 logical volume manager was replaced by LVM2, which has a more generic kernel framework than LVM1. LVM2 provides the following improvements over LVM1:
  • flexible capacity
  • more efficient metadata storage
  • better recovery format
  • new ASCII metadata format
  • atomic changes to metadata
  • redundant copies of metadata
LVM2 is backwards compatible with LVM1, with the exception of snapshot and cluster support. You can convert a volume group from LVM1 format to LVM2 format with the vgconvert command. For information on converting LVM metadata format, see the vgconvert(8) man page.
The underlying physical storage unit of an LVM logical volume is a block device such as a partition or whole disk. This device is initialized as an LVM physical volume (PV).
To create an LVM logical volume, the physical volumes are combined into a volume group (VG). This creates a pool of disk space out of which LVM logical volumes (LVs) can be allocated. This process is analogous to the way in which disks are divided into partitions. A logical volume is used by file systems and applications (such as databases).
Figure 2.1, “LVM Logical Volume Components” shows the components of a simple LVM logical volume:
LVM Logical Volume Components
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LVM Logical Volume Components

Figure 2.1. LVM Logical Volume Components

For detailed information on the components of an LVM logical volume, see Chapter 3, LVM Components.

2.4. The Clustered Logical Volume Manager (CLVM)
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The Clustered Logical Volume Manager (CLVM) is a set of clustering extensions to LVM. These extensions allow a cluster of computers to manage shared storage (for example, on a SAN) using LVM.
Whether you should use CLVM depends on your system requirements:
  • If only one node of your system requires access to the storage you are configuring as logical volumes, then you can use LVM without the CLVM extensions and the logical volumes created with that node are all local to the node.
  • If you are using a clustered system for failover where only a single node that accesses the storage is active at any one time, you should use High Availability Logical Volume Management agents (HA-LVM).
  • If more than one node of your cluster will require access to your storage which is then shared among the active nodes, then you must use CLVM. CLVM allows a user to configure logical volumes on shared storage by locking access to physical storage while a logical volume is being configured, and uses clustered locking services to manage the shared storage.
In order to use CLVM, the Red Hat Cluster Suite software, including the clvmd daemon, must be running. The clvmd daemon is the key clustering extension to LVM. The clvmd daemon runs in each cluster computer and distributes LVM metadata updates in a cluster, presenting each cluster computer with the same view of the logical volumes. For information on installing and administering Red Hat Cluster Suite, see Cluster Administration.
To ensure that clvmd is started at boot time, you can execute a chkconfig ... on command on the clvmd service, as follows: 
# chkconfig clvmd on
Copy to Clipboard Toggle word wrap
If the clvmd daemon has not been started, you can execute a service ... start command on the clvmd service, as follows: 
# service clvmd start
Copy to Clipboard Toggle word wrap
Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on a single node. There is no difference in the LVM commands themselves, or in the LVM graphical user interface, as described in Chapter 5, LVM Administration with CLI Commands and Chapter 8, LVM Administration with the LVM GUI. In order to enable the LVM volumes you are creating in a cluster, the cluster infrastructure must be running and the cluster must be quorate.
By default, logical volumes created with CLVM on shared storage are visible to all systems that have access to the shared storage. It is possible to create volume groups in which all of the storage devices are visible to only one node in the cluster. It is also possible to change the status of a volume group from a local volume group to a clustered volume group. For information, see Section 5.3.3, “Creating Volume Groups in a Cluster” and Section 5.3.8, “Changing the Parameters of a Volume Group”.

Warning

When you create volume groups with CLVM on shared storage, you must ensure that all nodes in the cluster have access to the physical volumes that constitute the volume group. Asymmmetric cluster configurations in which some nodes have access to the storage and others do not are not supported.
Figure 2.2, “CLVM Overview” shows a CLVM overview in a Red Hat cluster.
CLVM Overview
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CLVM Overview

Figure 2.2. CLVM Overview

Note

Shared storage for use in Red Hat Cluster Suite requires that you be running the cluster logical volume manager daemon (clvmd) or the High Availability Logical Volume Management agents (HA-LVM). If you are not able to use either the clvmd daemon or HA-LVM for operational reasons or because you do not have the correct entitlements, you must not use single-instance LVM on the shared disk as this may result in data corruption. If you have any concerns please contact your Red Hat service representative.

Note

CLVM requires changes to the lvm.conf file for cluster-wide locking. Information on configuring the lvm.conf file to support clustered locking is provided within the lvm.conf file itself. For information about the lvm.conf file, see Appendix B, The LVM Configuration Files.

2.5. Document Overview
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This remainder of this document includes the following chapters:

Chapter 3. LVM Components
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This chapter describes the components of an LVM Logical volume.

3.1. Physical Volumes
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The underlying physical storage unit of an LVM logical volume is a block device such as a partition or whole disk. To use the device for an LVM logical volume the device must be initialized as a physical volume (PV). Initializing a block device as a physical volume places a label near the start of the device.
By default, the LVM label is placed in the second 512-byte sector. You can overwrite this default by placing the label on any of the first 4 sectors. This allows LVM volumes to co-exist with other users of these sectors, if necessary.
An LVM label provides correct identification and device ordering for a physical device, since devices can come up in any order when the system is booted. An LVM label remains persistent across reboots and throughout a cluster.
The LVM label identifies the device as an LVM physical volume. It contains a random unique identifier (the UUID) for the physical volume. It also stores the size of the block device in bytes, and it records where the LVM metadata will be stored on the device.
The LVM metadata contains the configuration details of the LVM volume groups on your system. By default, an identical copy of the metadata is maintained in every metadata area in every physical volume within the volume group. LVM metadata is small and stored as ASCII.
Currently LVM allows you to store 0, 1 or 2 identical copies of its metadata on each physical volume. The default is 1 copy. Once you configure the number of metadata copies on the physical volume, you cannot change that number at a later time. The first copy is stored at the start of the device, shortly after the label. If there is a second copy, it is placed at the end of the device. If you accidentally overwrite the area at the beginning of your disk by writing to a different disk than you intend, a second copy of the metadata at the end of the device will allow you to recover the metadata.
For detailed information about the LVM metadata and changing the metadata parameters, see Appendix D, LVM Volume Group Metadata.

3.1.1. LVM Physical Volume Layout
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Figure 3.1, “Physical Volume layout” shows the layout of an LVM physical volume. The LVM label is on the second sector, followed by the metadata area, followed by the usable space on the device.

Note

In the Linux kernel (and throughout this document), sectors are considered to be 512 bytes in size.
Physical Volume layout
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Physical Volume layout

Figure 3.1. Physical Volume layout

3.1.2. Multiple Partitions on a Disk
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LVM allows you to create physical volumes out of disk partitions. It is generally recommended that you create a single partition that covers the whole disk to label as an LVM physical volume for the following reasons:
  • Administrative convenience
    It is easier to keep track of the hardware in a system if each real disk only appears once. This becomes particularly true if a disk fails. In addition, multiple physical volumes on a single disk may cause a kernel warning about unknown partition types at boot-up.
  • Striping performance
    LVM cannot tell that two physical volumes are on the same physical disk. If you create a striped logical volume when two physical volumes are on the same physical disk, the stripes could be on different partitions on the same disk. This would result in a decrease in performance rather than an increase.
Although it is not recommended, there may be specific circumstances when you will need to divide a disk into separate LVM physical volumes. For example, on a system with few disks it may be necessary to move data around partitions when you are migrating an existing system to LVM volumes. Additionally, if you have a very large disk and want to have more than one volume group for administrative purposes then it is necessary to partition the disk. If you do have a disk with more than one partition and both of those partitions are in the same volume group, take care to specify which partitions are to be included in a logical volume when creating striped volumes.

3.2. Volume Groups
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Physical volumes are combined into volume groups (VGs). This creates a pool of disk space out of which logical volumes can be allocated.
Within a volume group, the disk space available for allocation is divided into units of a fixed-size called extents. An extent is the smallest unit of space that can be allocated. Within a physical volume, extents are referred to as physical extents.
A logical volume is allocated into logical extents of the same size as the physical extents. The extent size is thus the same for all logical volumes in the volume group. The volume group maps the logical extents to physical extents.

3.3. LVM Logical Volumes
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In LVM, a volume group is divided up into logical volumes. There are three types of LVM logical volumes: linear volumes, striped volumes, and mirrored volumes. These are described in the following sections.

3.3.1. Linear Volumes
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A linear volume aggregates space from one or more physical volumes into one logical volume. For example, if you have two 60GB disks, you can create a 120GB logical volume. The physical storage is concatenated.
Creating a linear volume assigns a range of physical extents to an area of a logical volume in order. For example, as shown in Figure 3.2, “Extent Mapping” logical extents 1 to 99 could map to one physical volume and logical extents 100 to 198 could map to a second physical volume. From the point of view of the application, there is one device that is 198 extents in size.
Extent Mapping
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Extent Mapping

Figure 3.2. Extent Mapping

The physical volumes that make up a logical volume do not have to be the same size. Figure 3.3, “Linear Volume with Unequal Physical Volumes” shows volume group VG1 with a physical extent size of 4MB. This volume group includes 2 physical volumes named PV1 and PV2. The physical volumes are divided into 4MB units, since that is the extent size. In this example, PV1 is 200 extents in size (800MB) and PV2 is 100 extents in size (400MB). You can create a linear volume any size between 1 and 300 extents (4MB to 1200MB). In this example, the linear volume named LV1 is 300 extents in size.
Linear Volume with Unequal Physical Volumes
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Linear Volume with Unequal Physical Volumes

Figure 3.3. Linear Volume with Unequal Physical Volumes

You can configure more than one linear logical volume of whatever size you require from the pool of physical extents. Figure 3.4, “Multiple Logical Volumes” shows the same volume group as in Figure 3.3, “Linear Volume with Unequal Physical Volumes”, but in this case two logical volumes have been carved out of the volume group: LV1, which is 250 extents in size (1000MB) and LV2 which is 50 extents in size (200MB).
Multiple Logical Volumes
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Multiple Logical Volumes

Figure 3.4. Multiple Logical Volumes

3.3.2. Striped Logical Volumes
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When you write data to an LVM logical volume, the file system lays the data out across the underlying physical volumes. You can control the way the data is written to the physical volumes by creating a striped logical volume. For large sequential reads and writes, this can improve the efficiency of the data I/O.
Striping enhances performance by writing data to a predetermined number of physical volumes in round-robin fashion. With striping, I/O can be done in parallel. In some situations, this can result in near-linear performance gain for each additional physical volume in the stripe.
The following illustration shows data being striped across three physical volumes. In this figure:
  • the first stripe of data is written to PV1
  • the second stripe of data is written to PV2
  • the third stripe of data is written to PV3
  • the fourth stripe of data is written to PV1
In a striped logical volume, the size of the stripe cannot exceed the size of an extent.
Striping Data Across Three PVs
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Striping Data Across Three PVs

Figure 3.5. Striping Data Across Three PVs

Striped logical volumes can be extended by concatenating another set of devices onto the end of the first set. In order to extend a striped logical volume, however, there must be enough free space on the underlying physical volumes that make up the volume group to support the stripe. For example, if you have a two-way stripe that uses up an entire volume group, adding a single physical volume to the volume group will not enable you to extend the stripe. Instead, you must add at least two physical volumes to the volume group. For more information on extending a striped volume, see Section 5.4.9, “Extending a Striped Volume”.

3.3.3. Mirrored Logical Volumes
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A mirror maintains identical copies of data on different devices. When data is written to one device, it is written to a second device as well, mirroring the data. This provides protection for device failures. When one leg of a mirror fails, the logical volume becomes a linear volume and can still be accessed.
LVM supports mirrored volumes. When you create a mirrored logical volume, LVM ensures that data written to an underlying physical volume is mirrored onto a separate physical volume. With LVM, you can create mirrored logical volumes with multiple mirrors.
An LVM mirror divides the device being copied into regions that are typically 512KB in size. LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or mirrors. This log can be kept on disk, which will keep it persistent across reboots, or it can be maintained in memory.
Figure 3.6, “Mirrored Logical Volume” shows a mirrored logical volume with one mirror. In this configuration, the log is maintained on disk.
Mirrored Logical Volume
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Mirrored Logical Volume

Figure 3.6. Mirrored Logical Volume

Note

As of the Red Hat Enterprise Linux 5.3 release, mirrored logical volumes are supported in a cluster.
For information on creating and modifying mirrors, see Section 5.4.1.3, “Creating Mirrored Volumes”.

3.3.4. Snapshot Volumes
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The LVM snapshot feature provides the ability to create virtual images of a device at a particular instant without causing a service interruption. When a change is made to the original device (the origin) after a snapshot is taken, the snapshot feature makes a copy of the changed data area as it was prior to the change so that it can reconstruct the state of the device.

Note

LVM snapshots are not supported across the nodes in a cluster. You cannot create a snapshot volume in a clustered volume group.
Because a snapshot copies only the data areas that change after the snapshot is created, the snapshot feature requires a minimal amount of storage. For example, with a rarely updated origin, 3-5 % of the origin's capacity is sufficient to maintain the snapshot.

Note

Snapshot copies of a file system are virtual copies, not actual media backup for a file system. Snapshots do not provide a substitute for a backup procedure.
The size of the snapshot governs the amount of space set aside for storing the changes to the origin volume. For example, if you made a snapshot and then completely overwrote the origin the snapshot would have to be at least as big as the origin volume to hold the changes. You need to dimension a snapshot according to the expected level of change. So for example a short-lived snapshot of a read-mostly volume, such as /usr, would need less space than a long-lived snapshot of a volume that sees a greater number of writes, such as /home.
If a snapshot runs full, the snapshot becomes invalid, since it can no longer track changes on the origin volumed. You should regularly monitor the size of the snapshot. Snapshots are fully resizeable, however, so if you have the storage capacity you can increase the size of the snapshot volume to prevent it from getting dropped. Conversely, if you find that the snapshot volume is larger than you need, you can reduce the size of the volume to free up space that is needed by other logical volumes.
When you create a snapshot file system, full read and write access to the origin stays possible. If a chunk on a snapshot is changed, that chunk is marked and never gets copied from the original volume.
There are several uses for the snapshot feature:
  • Most typically, a snapshot is taken when you need to perform a backup on a logical volume without halting the live system that is continuously updating the data.
  • You can execute the fsck command on a snapshot file system to check the file system integrity and determine whether the original file system requires file system repair.
  • Because the snapshot is read/write, you can test applications against production data by taking a snapshot and running tests against the snapshot, leaving the real data untouched.
  • You can create volumes for use with the Xen virtual machine monitor. You can use the snapshot feature to create a disk image, snapshot it, and modify the snapshot for a particular domU instance. You can then create another snapshot and modify it for another domU instance. Since the only storage used is chunks that were changed on the origin or snapshot, the majority of the volume is shared.

Chapter 4. LVM Administration Overview
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This chapter provides an overview of the administrative procedures you use to configure LVM logical volumes. This chapter is intended to provide a general understanding of the steps involved. For specific step-by-step examples of common LVM configuration procedures, see Chapter 6, LVM Configuration Examples.
For descriptions of the CLI commands you can use to perform LVM administration, see Chapter 5, LVM Administration with CLI Commands. Alternately, you can use the LVM GUI, which is described in Chapter 8, LVM Administration with the LVM GUI.

4.1. Creating LVM Volumes in a Cluster
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To create logical volumes in a cluster environment, you use the Clustered Logical Volume Manager (CLVM), which is a set of clustering extensions to LVM. These extensions allow a cluster of computers to manage shared storage (for example, on a SAN) using LVM. In order to use CLVM, the Red Hat Cluster Suite software, including the clvmd daemon, must be started at boot time, as described in Section 2.4, “The Clustered Logical Volume Manager (CLVM)”.
Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on a single node. There is no difference in the LVM commands themselves, or in the LVM GUI interface. In order to enable the LVM volumes you are creating in a cluster, the cluster infrastructure must be running and the cluster must be quorate.
CLVM requires changes to the lvm.conf file for cluster-wide locking. Information on configuring the lvm.conf file to support clustered locking is provided within the lvm.conf file itself. For information about the lvm.conf file, see Appendix B, The LVM Configuration Files.
By default, logical volumes created with CLVM on shared storage are visible to all systems that have access to the shared storage. It is possible to create volume groups in which all of the storage devices are visible to only one node in the cluster. It is also possible to change the status of a volume group from a local volume group to a clustered volume group. For information, see Section 5.3.3, “Creating Volume Groups in a Cluster” and Section 5.3.8, “Changing the Parameters of a Volume Group”

Warning

When you create volume groups with CLVM on shared storage, you must ensure that all nodes in the cluster have access to the physical volumes that constitute the volume group. Asymmmetric cluster configurations in which some nodes have access to the storage and others do not are not supported.

Note

Shared storage for use in Red Hat Cluster Suite requires that you be running the cluster logical volume manager daemon (clvmd) or the High Availability Logical Volume Management agents (HA-LVM). If you are not able to use either the clvmd daemon or HA-LVM for operational reasons or because you do not have the correct entitlements, you must not use single-instance LVM on the shared disk as this may result in data corruption. If you have any concerns please contact your Red Hat service representative.
For information on how to install Red Hat Cluster Suite and set up the cluster infrastructure, see Cluster Administration.
For an example of creating a mirrored logical volume in a cluster, see Section 6.5, “Creating a Mirrored LVM Logical Volume in a Cluster”.

4.2. Logical Volume Creation Overview
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The following is a summary of the steps to perform to create an LVM logical volume.
  1. Initialize the partitions you will use for the LVM volume as physical volumes (this labels them).
  2. Create a volume group.
  3. Create a logical volume.
After creating the logical volume you can create and mount the file system. The examples in this document use GFS file systems.
  1. Create a GFS file system on the logical volume with the gfs_mkfs command.
  2. Create a new mount point with the mkdir command. In a clustered system, create the mount point on all nodes in the cluster.
  3. Mount the file system. You may want to add a line to the fstab file for each node in the system.
Alternately, you can create and mount the GFS file system with the LVM GUI.
Creating the LVM volume is machine independent, since the storage area for LVM setup information is on the physical volumes and not the machine where the volume was created. Servers that use the storage have local copies, but can recreate that from what is on the physical volumes. You can attach physical volumes to a different server if the LVM versions are compatible.

4.3. Growing a File System on a Logical Volume
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To grow a file system on a logical volume, perform the following steps:
  1. Make a new physical volume.
  2. Extend the volume group that contains the logical volume with the file system you are growing to include the new physical volume.
  3. Extend the logical volume to include the new physical volume.
  4. Grow the file system.
If you have sufficient unallocated space in the volume group, you can use that space to extend the logical volume instead of performing steps 1 and 2.

4.4. Logical Volume Backup
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Metadata backups and archives are automatically created on every volume group and logical volume configuration change unless disabled in the lvm.conf file. By default, the metadata backup is stored in the /etc/lvm/backup file and the metadata archives are stored in the /etc/lvm/archive file. How long the metadata archives stored in the /etc/lvm/archive file are kept and how many archive files are kept is determined by parameters you can set in the lvm.conf file. A daily system backup should include the contents of the /etc/lvm directory in the backup.
Note that a metadata backup does not back up the user and system data contained in the logical volumes.
You can manually back up the metadata to the /etc/lvm/backup file with the vgcfgbackup command. You can restore metadata with the vgcfgrestore command. The vgcfgbackup and vgcfgrestore commands are described in Section 5.3.13, “Backing Up Volume Group Metadata”.

4.5. Logging
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All message output passes through a logging module with independent choices of logging levels for:
  • standard output/error
  • syslog
  • log file
  • external log function
The logging levels are set in the /etc/lvm/lvm.conf file, which is described in Appendix B, The LVM Configuration Files.

4.6. Online Device Reconfiguration
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When you change your hardware configuration after system bootup and add or delete a device on a node, you may need to update the LVM cache file, which maintains a listing of current LVM devices. For example, when you add new disks to the system on a SAN or hotplug a new disk that is an LVM physical volume, you may need to update this file.
You can update the LVM cache file by running the vgscan command. For information on the vgscan command and the LVM cache file, see Section 5.3.6, “Scanning Disks for Volume Groups to Build the Cache File”.

Chapter 5. LVM Administration with CLI Commands
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This chapter summarizes the individual administrative tasks you can perform with the LVM Command Line Interface (CLI) commands to create and maintain logical volumes.

Note

If you are creating or modifying an LVM volume for a clustered environment, you must ensure that you are running the clvmd daemon. For information, see Section 4.1, “Creating LVM Volumes in a Cluster”.

5.1. Using CLI Commands
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There are several general features of all LVM CLI commands.
When sizes are required in a command line argument, units can always be specified explicitly. If you do not specify a unit, then a default is assumed, usually KB or MB. LVM CLI commands do not accept fractions.
When specifying units in a command line argument, LVM is case-insensitive; specifying M or m is equivalent, for example, and powers of 2 (multiples of 1024) are used. However, when specifying the --units argument in a command, lower-case indicates that units are in multiples of 1024 while upper-case indicates that units are in multiples of 1000.
Where commands take volume group or logical volume names as arguments, the full path name is optional. A logical volume called lvol0 in a volume group called vg0 can be specified as vg0/lvol0. Where a list of volume groups is required but is left empty, a list of all volume groups will be substituted. Where a list of logical volumes is required but a volume group is given, a list of all the logical volumes in that volume group will be substituted. For example, the lvdisplay vg0 command will display all the logical volumes in volume group vg0.
All LVM commands accept a -v argument, which can be entered multiple times to increase the output verbosity. For example, the following examples shows the default output of the lvcreate command. 
# lvcreate -L 50MB new_vg
  Rounding up size to full physical extent 52.00 MB
  Logical volume "lvol0" created
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The following command shows the output of the lvcreate command with the -v argument. 
# lvcreate -v -L 50MB new_vg
    Finding volume group "new_vg"
  Rounding up size to full physical extent 52.00 MB
    Archiving volume group "new_vg" metadata (seqno 4).
    Creating logical volume lvol0
    Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
    Found volume group "new_vg"
    Creating new_vg-lvol0
    Loading new_vg-lvol0 table
    Resuming new_vg-lvol0 (253:2)
    Clearing start of logical volume "lvol0"
    Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
  Logical volume "lvol0" created
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You could also have used the -vv, -vvv or the -vvvv argument to display increasingly more details about the command execution. The -vvvv argument provides the maximum amount of information at this time. The following example shows only the first few lines of output for the lvcreate command with the -vvvv argument specified. 
# lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:913         Processing: lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:916         O_DIRECT will be used
#config/config.c:864       Setting global/locking_type to 1
#locking/locking.c:138       File-based locking selected.
#config/config.c:841       Setting global/locking_dir to /var/lock/lvm
#activate/activate.c:358       Getting target version for linear
#ioctl/libdm-iface.c:1569         dm version   OF   [16384]
#ioctl/libdm-iface.c:1569         dm versions   OF   [16384]
#activate/activate.c:358       Getting target version for striped
#ioctl/libdm-iface.c:1569         dm versions   OF   [16384]
#config/config.c:864       Setting activation/mirror_region_size to 512
...
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You can display help for any of the LVM CLI commands with the --help argument of the command. 
# commandname --help
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To display the man page for a command, execute the man command: 
# man commandname
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The man lvm command provides general online information about LVM.
All LVM objects are referenced internally by a UUID, which is assigned when you create the object. This can be useful in a situation where you remove a physical volume called /dev/sdf which is part of a volume group and, when you plug it back in, you find that it is now /dev/sdk. LVM will still find the physical volume because it identifies the physical volume by its UUID and not its device name. For information on specifying the UUID of a physical volume when creating a physical volume, see Section 7.4, “Recovering Physical Volume Metadata”.

5.2. Physical Volume Administration
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This section describes the commands that perform the various aspects of physical volume administration.

5.2.1. Creating Physical Volumes
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The following subsections describe the commands used for creating physical volumes.
5.2.1.1. Setting the Partition Type
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If you are using a whole disk device for your physical volume, the disk must have no partition table. For DOS disk partitions, the partition id should be set to 0x8e using the fdisk or cfdisk command or an equivalent. For whole disk devices only the partition table must be erased, which will effectively destroy all data on that disk. You can remove an existing partition table by zeroing the first sector with the following command: 
# dd if=/dev/zero of=PhysicalVolume bs=512 count=1
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5.2.1.2. Initializing Physical Volumes
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Use the pvcreate command to initialize a block device to be used as a physical volume. Initialization is analogous to formatting a file system.
The following command initializes /dev/sdd, /dev/sde, and /dev/sdf as LVM physical volumes for later use as part of LVM logical volumes. 
# pvcreate /dev/sdd /dev/sde /dev/sdf
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To initialize partitions rather than whole disks: run the pvcreate command on the partition. The following example initializes the partition /dev/hdb1 as an LVM physical volume for later use as part of an LVM logical volume. 
# pvcreate /dev/hdb1
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5.2.1.3. Scanning for Block Devices
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You can scan for block devices that may be used as physical volumes with the lvmdiskscan command, as shown in the following example. 
# lvmdiskscan
/dev/ram0                    [       16.00 MB]
  /dev/sda                     [       17.15 GB]
  /dev/root                    [       13.69 GB]
  /dev/ram                     [       16.00 MB]
  /dev/sda1                    [       17.14 GB] LVM physical volume
  /dev/VolGroup00/LogVol01     [      512.00 MB]
  /dev/ram2                    [       16.00 MB]
  /dev/new_vg/lvol0            [       52.00 MB]
  /dev/ram3                    [       16.00 MB]
  /dev/pkl_new_vg/sparkie_lv   [        7.14 GB]
  /dev/ram4                    [       16.00 MB]
  /dev/ram5                    [       16.00 MB]
  /dev/ram6                    [       16.00 MB]
  /dev/ram7                    [       16.00 MB]
  /dev/ram8                    [       16.00 MB]
  /dev/ram9                    [       16.00 MB]
  /dev/ram10                   [       16.00 MB]
  /dev/ram11                   [       16.00 MB]
  /dev/ram12                   [       16.00 MB]
  /dev/ram13                   [       16.00 MB]
  /dev/ram14                   [       16.00 MB]
  /dev/ram15                   [       16.00 MB]
  /dev/sdb                     [       17.15 GB]
  /dev/sdb1                    [       17.14 GB] LVM physical volume
  /dev/sdc                     [       17.15 GB]
  /dev/sdc1                    [       17.14 GB] LVM physical volume
  /dev/sdd                     [       17.15 GB]
  /dev/sdd1                    [       17.14 GB] LVM physical volume
  7 disks
  17 partitions
  0 LVM physical volume whole disks
  4 LVM physical volumes
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5.2.2. Displaying Physical Volumes
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There are three commands you can use to display properties of LVM physical volumes: pvs, pvdisplay, and pvscan.
The pvs command provides physical volume information in a configurable form, displaying one line per physical volume. The pvs command provides a great deal of format control, and is useful for scripting. For information on using the pvs command to customize your output, see Section 5.9, “Customized Reporting for LVM”.
The pvdisplay command provides a verbose multi-line output for each physical volume. It displays physical properties (size, extents, volume group, etc.) in a fixed format.
The following example shows the output of the pvdisplay command for a single physical volume. 
# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sdc1
  VG Name               new_vg
  PV Size               17.14 GB / not usable 3.40 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              4388
  Free PE               4375
  Allocated PE          13
  PV UUID               Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe
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The pvscan command scans all supported LVM block devices in the system for physical volumes.
The following command shows all physical devices found: 
# pvscan
 PV /dev/sdb2   VG vg0   lvm2 [964.00 MB / 0   free]
 PV /dev/sdc1   VG vg0   lvm2 [964.00 MB / 428.00 MB free]
 PV /dev/sdc2            lvm2 [964.84 MB]
 Total: 3 [2.83 GB] / in use: 2 [1.88 GB] / in no VG: 1 [964.84 MB]
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You can define a filter in the lvm.conf so that this command will avoid scanning specific physical volumes. For information on using filters to control which devices are scanned, see Section 5.6, “Controlling LVM Device Scans with Filters”.

5.2.3. Preventing Allocation on a Physical Volume
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You can prevent allocation of physical extents on the free space of one or more physical volumes with the pvchange command. This may be necessary if there are disk errors, or if you will be removing the physical volume.
The following command disallows the allocation of physical extents on /dev/sdk1. 
# pvchange -x n /dev/sdk1
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You can also use the -xy arguments of the pvchange command to allow allocation where it had previously been disallowed.

5.2.4. Resizing a Physical Volume
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If you need to change the size of an underlying block device for any reason, use the pvresize command to update LVM with the new size. You can execute this command while LVM is using the physical volume.

5.2.5. Removing Physical Volumes
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If a device is no longer required for use by LVM, you can remove the LVM label with the pvremove command. Executing the pvremove command zeroes the LVM metadata on an empty physical volume.
If the physical volume you want to remove is currently part of a volume group, you must remove it from the volume group with the vgreduce command, as described in Section 5.3.7, “Removing Physical Volumes from a Volume Group”. 
# pvremove /dev/ram15
  Labels on physical volume "/dev/ram15" successfully wiped
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5.3. Volume Group Administration
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This section describes the commands that perform the various aspects of volume group administration.

5.3.1. Creating Volume Groups
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To create a volume group from one or more physical volumes, use the vgcreate command. The vgcreate command creates a new volume group by name and adds at least one physical volume to it.
The following command creates a volume group named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1. 
# vgcreate vg1 /dev/sdd1 /dev/sde1
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When physical volumes are used to create a volume group, its disk space is divided into 4 MB extents, by default. This extent is the minimum amount by which the logical volume may be increased or decreased in size. Large numbers of extents will have no impact on I/O performance of the logical volume.
You can specify the extent size with the -s option to the vgcreate command if the default extent size is not suitable. You can put limits on the number of physical or logical volumes the volume group can have by using the -p and -l arguments of the vgcreate command.
By default, a volume group allocates physical extents according to common-sense rules such as not placing parallel stripes on the same physical volume. This is the normal allocation policy. You can use the --alloc argument of the vgcreate command to specify an allocation policy of contiguous, anywhere, or cling.
The contiguous policy requires that new extents are adjacent to existing extents. If there are sufficient free extents to satisfy an allocation request but a normal allocation policy would not use them, the anywhere allocation policy will, even if that reduces performance by placing two stripes on the same physical volume. The cling policy places new extents on the same physical volume as existing extents in the same stripe of the logical volume. These policies can be changed using the vgchange command.
For information on using the cling policy in conjunction with LVM tags to specify which additional physical volumes to use when extending an LVM volume, see Section 5.4.11, “Extending a Logical Volume with the cling Allocation Policy”.
In general, allocation policies other than normal are required only in special cases where you need to specify unusual or nonstandard extent allocation.
LVM volume groups and underlying logical volumes are included in the device special file directory tree in the /dev directory with the following layout: 
/dev/vg/lv/
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For example, if you create two volume groups myvg1 and myvg2, each with three logical volumes named lv01, lv02, and lv03, this creates six device special files: 
/dev/myvg1/lv01
/dev/myvg1/lv02
/dev/myvg1/lv03
/dev/myvg2/lv01
/dev/myvg2/lv02
/dev/myvg2/lv03
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The maximum device size with LVM is 8 Exabytes on 64-bit CPUs.

5.3.2. LVM Allocation
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When an LVM operation needs to allocate physical extents for one or more logical volumes, the allocation proceeds as follows:
  • The complete set of unallocated physical extents in the volume group is generated for consideration. If you supply any ranges of physical extents at the end of the command line, only unallocated physical extents within those ranges on the specified physical volumes are considered.
  • Each allocation policy is tried in turn, starting with the strictest policy (contiguous) and ending with the allocation policy specified using the --alloc option or set as the default for the particular logical volume or volume group. For each policy, working from the lowest-numbered logical extent of the empty logical volume space that needs to be filled, as much space as possible is allocated, according to the restrictions imposed by the allocation policy. If more space is needed, LVM moves on to the next policy.
The allocation policy restrictions are as follows:
  • An allocation policy of contiguous requires that the physical location of any logical extent that is not the first logical extent of a logical volume is adjacent to the physical location of the logical extent immediately preceding it.
    When a logical volume is striped or mirrored, the contiguous allocation restriction is applied independently to each stripe or mirror image (leg) that needs space.
  • An allocation policy of cling requires that the physical volume used for any logical extent to be added to an existing logical volume is already in use by at least one logical extent earlier in that logical volume. If the configuration parameter allocation/cling_tag_list is defined, then two physical volumes are considered to match if any of the listed tags is present on both physical volumes. This allows groups of physical volumes with similar properties (such as their physical location) to be tagged and treated as equivalent for allocation purposes. For more information on using the cling policy in conjunction with LVM tags to specify which additional physical volumes to use when extending an LVM volume, see Section 5.4.11, “Extending a Logical Volume with the cling Allocation Policy”.
    When a Logical Volume is striped or mirrored, the cling allocation restriction is applied independently to each stripe or mirror image (leg) that needs space.
  • An allocation policy of normal will not choose a physical extent that shares the same physical volume as a logical extent already allocated to a parallel logical volume (that is, a different stripe or mirror image/leg) at the same offset within that parallel logical volume.
    When allocating a mirror log at the same time as logical volumes to hold the mirror data, an allocation policy of normal will first try to select different physical volumes for the log and the data. If that is not possible and the allocation/mirror_logs_require_separate_pvs configuration parameter is set to 0, it will then allow the log to share physical volume(s) with part of the data.
  • If there are sufficient free extents to satisfy an allocation request but a normal allocation policy would not use them, the anywhere allocation policy will, even if that reduces performance by placing two stripes on the same physical volume.
The allocation policies can be changed using the vgchange command.

Note

If you rely upon any layout behaviour beyond that documented in this section according to the defined allocation policies, you should note that this might change in future versions of the code. For example, if you supply on the command line two empty physical volumes that have an identical number of free physical extents available for allocation, LVM currently considers using each of them in the order they are listed; there is no guarantee that future releases will maintain that property. If it is important to obtain a specific layout for a particular Logical Volume, then you should build it up through a sequence of lvcreate and lvconvert steps such that the allocation policies applied to each step leave LVM no discretion over the layout.
To view the way the allocation process currently works in any specific case, you can read the debug logging output, for example by adding the -vvvv option to a command.

5.3.3. Creating Volume Groups in a Cluster
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You create volume groups in a cluster environment with the vgcreate command, just as you create them on a single node.
By default, volume groups created with CLVM on shared storage are visible to all computers that have access to the shared storage. It is possible, however, to create volume groups that are local, visible only to one node in the cluster, by using the -c n of the vgcreate command.
The following command, when executed in a cluster environment, creates a volume group that is local to the node from which the command was executed. The command creates a local volume named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1. 
#  vgcreate -c n vg1 /dev/sdd1 /dev/sde1
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You can change whether an existing volume group is local or clustered with the -c option of the vgchange command, which is described in Section 5.3.8, “Changing the Parameters of a Volume Group”.
You can check whether an existing volume group is a clustered volume group with the vgs command, which displays the c attribute if the volume is clustered. The following command displays the attributes of the volume groups VolGroup00 and testvg1. In this example, VolGroup00 is not clustered, while testvg1 is clustered, as indicated by the c attribute under the Attr heading. 
# vgs
  VG            #PV #LV #SN Attr   VSize  VFree
  VolGroup00      1   2   0 wz--n- 19.88G    0
  testvg1         1   1   0 wz--nc 46.00G 8.00M
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For more information on the vgs command, see Section 5.3.5, “Displaying Volume Groups”Section 5.9, “Customized Reporting for LVM”, and the vgs man page.

5.3.4. Adding Physical Volumes to a Volume Group
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To add additional physical volumes to an existing volume group, use the vgextend command. The vgextend command increases a volume group's capacity by adding one or more free physical volumes.
The following command adds the physical volume /dev/sdf1 to the volume group vg1. 
# vgextend vg1 /dev/sdf1
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5.3.5. Displaying Volume Groups
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There are two commands you can use to display properties of LVM volume groups: vgs and vgdisplay.
The vgscan command, which scans all the disks for volume groups and rebuilds the LVM cache file, also displays the volume groups. For information on the vgscan command, see Section 5.3.6, “Scanning Disks for Volume Groups to Build the Cache File”.
The vgs command provides volume group information in a configurable form, displaying one line per volume group. The vgs command provides a great deal of format control, and is useful for scripting. For information on using the vgs command to customize your output, see Section 5.9, “Customized Reporting for LVM”.
The vgdisplay command displays volume group properties (such as size, extents, number of physical volumes, etc.) in a fixed form. The following example shows the output of a vgdisplay command for the volume group new_vg. If you do not specify a volume group, all existing volume groups are displayed. 
# vgdisplay new_vg
  --- Volume group ---
  VG Name               new_vg
  System ID
  Format                lvm2
  Metadata Areas        3
  Metadata Sequence No  11
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               0
  Max PV                0
  Cur PV                3
  Act PV                3
  VG Size               51.42 GB
  PE Size               4.00 MB
  Total PE              13164
  Alloc PE / Size       13 / 52.00 MB
  Free  PE / Size       13151 / 51.37 GB
  VG UUID               jxQJ0a-ZKk0-OpMO-0118-nlwO-wwqd-fD5D32
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The vgscan command scans all supported disk devices in the system looking for LVM physical volumes and volume groups. This builds the LVM cache in the /etc/lvm/.cache file, which maintains a listing of current LVM devices.
LVM runs the vgscan command automatically at system startup and at other times during LVM operation, such as when you execute a vgcreate command or when LVM detects an inconsistency.

Note

You may need to run the vgscan command manually when you change your hardware configuration and add or delete a device from a node, causing new devices to be visible to the system that were not present at system bootup. This may be necessary, for example, when you add new disks to the system on a SAN or hotplug a new disk that has been labeled as a physical volume.
You can define a filter in the lvm.conf file to restrict the scan to avoid specific devices. For information on using filters to control which devices are scanned, see Section 5.6, “Controlling LVM Device Scans with Filters”.
The following example shows the output of a vgscan command. 
# vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "new_vg" using metadata type lvm2
  Found volume group "officevg" using metadata type lvm2
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To remove unused physical volumes from a volume group, use the vgreduce command. The vgreduce command shrinks a volume group's capacity by removing one or more empty physical volumes. This frees those physical volumes to be used in different volume groups or to be removed from the system.
Before removing a physical volume from a volume group, you can make sure that the physical volume is not used by any logical volumes by using the pvdisplay command. 
# pvdisplay /dev/hda1

-- Physical volume ---
PV Name               /dev/hda1
VG Name               myvg
PV Size               1.95 GB / NOT usable 4 MB [LVM: 122 KB]
PV#                   1
PV Status             available
Allocatable           yes (but full)
Cur LV                1
PE Size (KByte)       4096
Total PE              499
Free PE               0
Allocated PE          499
PV UUID               Sd44tK-9IRw-SrMC-MOkn-76iP-iftz-OVSen7
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If the physical volume is still being used you will have to migrate the data to another physical volume using the pvmove command. Then use the vgreduce command to remove the physical volume:
The following command removes the physical volume /dev/hda1 from the volume group my_volume_group. 
# vgreduce my_volume_group /dev/hda1
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5.3.8. Changing the Parameters of a Volume Group
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The vgchange command is used to deactivate and activate volume groups, as described in Section 5.3.9, “Activating and Deactivating Volume Groups”. You can also use this command to change several volume group parameters for an existing volume group.
The following command changes the maximum number of logical volumes of volume group vg00 to 128. 
# vgchange -l 128 /dev/vg00
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For a description of the volume group parameters you can change with the vgchange command, see the vgchange(8) man page.

5.3.9. Activating and Deactivating Volume Groups
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When you create a volume group it is, by default, activated. This means that the logical volumes in that group are accessible and subject to change.
There are various circumstances for which you need to make a volume group inactive and thus unknown to the kernel. To deactivate or activate a volume group, use the -a (--available) argument of the vgchange command.
The following example deactivates the volume group my_volume_group. 
# vgchange -a n my_volume_group
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If clustered locking is enabled, add ’e’ to activate or deactivate a volume group exclusively on one node or ’l’ to activate or/deactivate a volume group only on the local node. Logical volumes with single-host snapshots are always activated exclusively because they can only be used on one node at once.
You can deactivate individual logical volumes with the lvchange command, as described in Section 5.4.4, “Changing the Parameters of a Logical Volume Group”, For information on activating logical volumes on individual nodes in a cluster, see Section 5.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.

5.3.10. Removing Volume Groups
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To remove a volume group that contains no logical volumes, use the vgremove command. 
# vgremove officevg
  Volume group "officevg" successfully removed
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5.3.11. Splitting a Volume Group
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To split the physical volumes of a volume group and create a new volume group, use the vgsplit command.
Logical volumes cannot be split between volume groups. Each existing logical volume must be entirely on the physical volumes forming either the old or the new volume group. If necessary, however, you can use the pvmove command to force the split.
The following example splits off the new volume group smallvg from the original volume group bigvg. 
# vgsplit bigvg smallvg /dev/ram15
  Volume group "smallvg" successfully split from "bigvg"
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5.3.12. Combining Volume Groups
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To combine two volume groups into a single volume group, use the vgmerge command. You can merge an inactive "source" volume with an active or an inactive "destination" volume if the physical extent sizes of the volume are equal and the physical and logical volume summaries of both volume groups fit into the destination volume groups limits.
The following command merges the inactive volume group my_vg into the active or inactive volume group databases giving verbose runtime information. 
# vgmerge -v databases my_vg
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5.3.13. Backing Up Volume Group Metadata
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Metadata backups and archives are automatically created on every volume group and logical volume configuration change unless disabled in the lvm.conf file. By default, the metadata backup is stored in the /etc/lvm/backup file and the metadata archives are stored in the /etc/lvm/archives file. You can manually back up the metadata to the /etc/lvm/backup file with the vgcfgbackup command.
The vgcfrestore command restores the metadata of a volume group from the archive to all the physical volumes in the volume groups.
For an example of using the vgcfgrestore command to recover physical volume metadata, see Section 7.4, “Recovering Physical Volume Metadata”.

5.3.14. Renaming a Volume Group
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Use the vgrename command to rename an existing volume group.
Either of the following commands renames the existing volume group vg02 to my_volume_group 
# vgrename /dev/vg02 /dev/my_volume_group
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# vgrename vg02 my_volume_group
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5.3.15. Moving a Volume Group to Another System
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You can move an entire LVM volume group to another system. It is recommended that you use the vgexport and vgimport commands when you do this.
The vgexport command makes an inactive volume group inaccessible to the system, which allows you to detach its physical volumes. The vgimport command makes a volume group accessible to a machine again after the vgexport command has made it inactive.
To move a volume group form one system to another, perform the following steps:
  1. Make sure that no users are accessing files on the active volumes in the volume group, then unmount the logical volumes.
  2. Use the -a n argument of the vgchange command to mark the volume group as inactive, which prevents any further activity on the volume group.
  3. Use the vgexport command to export the volume group. This prevents it from being accessed by the system from which you are removing it.
    After you export the volume group, the physical volume will show up as being in an exported volume group when you execute the pvscan command, as in the following example. 
    # pvscan
  PV /dev/sda1    is in exported VG myvg [17.15 GB / 7.15 GB free]
  PV /dev/sdc1    is in exported VG myvg [17.15 GB / 15.15 GB free]
  PV /dev/sdd1   is in exported VG myvg [17.15 GB / 15.15 GB free]
  ...
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    When the system is next shut down, you can unplug the disks that constitute the volume group and connect them to the new system.
  4. When the disks are plugged into the new system, use the vgimport command to import the volume group, making it accessible to the new system.
  5. Activate the volume group with the -a y argument of the vgchange command.
  6. Mount the file system to make it available for use.

5.3.16. Recreating a Volume Group Directory
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To recreate a volume group directory and logical volume special files, use the vgmknodes command. This command checks the LVM2 special files in the /dev directory that are needed for active logical volumes. It creates any special files that are missing removes unused ones.
You can incorporate the vgmknodes command into the vgscan command by specifying the mknodes argument to the vgscan command.

5.4. Logical Volume Administration
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This section describes the commands that perform the various aspects of logical volume administration.

5.4.1. Creating Logical Volumes
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To create a logical volume, use the lvcreate command. You can create linear volumes, striped volumes, and mirrored volumes, as described in the following subsections.
If you do not specify a name for the logical volume, the default name lvol# is used where # is the internal number of the logical volume.
The following sections provide examples of logical volume creation for the three types of logical volumes you can create with LVM.
5.4.1.1. Creating Linear Volumes
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When you create a logical volume, the logical volume is carved from a volume group using the free extents on the physical volumes that make up the volume group. Normally logical volumes use up any space available on the underlying physical volumes on a next-free basis. Modifying the logical volume frees and reallocates space in the physical volumes.
The following command creates a logical volume 10 gigabytes in size in the volume group vg1. 
# lvcreate -L 10G vg1
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The following command creates a 1500 MB linear logical volume named testlv in the volume group testvg, creating the block device /dev/testvg/testlv. 
# lvcreate -L1500 -n testlv testvg
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The following command creates a 50 gigabyte logical volume named gfslv from the free extents in volume group vg0. 
# lvcreate -L 50G -n gfslv vg0
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You can use the -l argument of the lvcreate command to specify the size of the logical volume in extents. You can also use this argument to specify the percentage of the volume group to use for the logical volume. The following command creates a logical volume called mylv that uses 60% of the total space in volume group testvg. 
# lvcreate -l 60%VG -n mylv testvg
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You can also use the -l argument of the lvcreate command to specify the percentage of the remaining free space in a volume group as the size of the logical volume. The following command creates a logical volume called yourlv that uses all of the unallocated space in the volume group testvg. 
# lvcreate -l 100%FREE -n yourlv testvg
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You can use -l argument of the lvcreate command to create a logical volume that uses the entire volume group. Another way to create a logical volume that uses the entire volume group is to use the vgdisplay command to find the "Total PE" size and to use those results as input to the lvcreate command.
The following commands create a logical volume called mylv that fills the volume group named testvg. 
# vgdisplay testvg | grep "Total PE"
Total PE              10230
# lvcreate -l 10230 testvg -n mylv
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The underlying physical volumes used to create a logical volume can be important if the physical volume needs to be removed, so you may need to consider this possibility when you create the logical volume. For information on removing a physical volume from a volume group, see Section 5.3.7, “Removing Physical Volumes from a Volume Group”.
To create a logical volume to be allocated from a specific physical volume in the volume group, specify the physical volume or volumes at the end at the lvcreate command line. The following command creates a logical volume named testlv in volume group testvg allocated from the physical volume /dev/sdg1, 
# lvcreate -L 1500 -ntestlv testvg /dev/sdg1
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You can specify which extents of a physical volume are to be used for a logical volume. The following example creates a linear logical volume out of extents 0 through 24 of physical volume /dev/sda1 and extents 50 through 124 of physical volume /dev/sdb1 in volume group testvg. 
# lvcreate -l 100 -n testlv testvg /dev/sda1:0-24 /dev/sdb1:50-124
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The following example creates a linear logical volume out of extents 0 through 24 of physical volume /dev/sda1 and then continues laying out the logical volume at extent 100. 
# lvcreate -l 100 -n testlv testvg /dev/sda1:0-24:100-
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The default policy for how the extents of a logical volume are allocated is inherit, which applies the same policy as for the volume group. These policies can be changed using the lvchange command. For information on allocation policies, see Section 5.3.1, “Creating Volume Groups”.
5.4.1.2. Creating Striped Volumes
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For large sequential reads and writes, creating a striped logical volume can improve the efficiency of the data I/O. For general information about striped volumes, see Section 3.3.2, “Striped Logical Volumes”.
When you create a striped logical volume, you specify the number of stripes with the -i argument of the lvcreate command. This determines over how many physical volumes the logical volume will be striped. The number of stripes cannot be greater than the number of physical volumes in the volume group (unless the --alloc anywhere argument is used).
If the underlying physical devices that make up a striped logical volume are different sizes, the maximum size of the striped volume is determined by the smallest underlying device. For example, in a two-legged stripe, the maximum size is twice the size of the smaller device. In a three-legged stripe, the maximum size is three times the size of the smallest device.
The following command creates a striped logical volume across 2 physical volumes with a stripe of 64kB. The logical volume is 50 gigabytes in size, is named gfslv, and is carved out of volume group vg0. 
# lvcreate -L 50G -i2 -I64 -n gfslv vg0
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As with linear volumes, you can specify the extents of the physical volume that you are using for the stripe. The following command creates a striped volume 100 extents in size that stripes across two physical volumes, is named stripelv and is in volume group testvg. The stripe will use sectors 0-49 of /dev/sda1 and sectors 50-99 of /dev/sdb1. 
# lvcreate -l 100 -i2 -nstripelv testvg /dev/sda1:0-49 /dev/sdb1:50-99
  Using default stripesize 64.00 KB
  Logical volume "stripelv" created
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5.4.1.3. Creating Mirrored Volumes
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Note

As of the Red Hat Enterprise Linux 5.3 release, mirrored logical volumes are supported in a cluster. Creating a mirrored LVM logical volume in a cluster requires the same commands and procedures as creating a mirrored LVM logical volume on a single node. However, in order to create a mirrored LVM volume in a cluster the cluster and cluster mirror infrastructure must be running, the cluster must be quorate, and the locking type in the lvm.conf file must be set correctly to enable cluster locking. For an example of creating a mirrored volume in a cluster, see Section 6.5, “Creating a Mirrored LVM Logical Volume in a Cluster”.
When you create a mirrored volume, you specify the number of copies of the data to make with the -m argument of the lvcreate command. Specifying -m1 creates one mirror, which yields two copies of the file system: a linear logical volume plus one copy. Similarly, specifying -m2 creates two mirrors, yielding three copies of the file system.
The following command creates a mirrored logical volume with a single mirror. The volume is 50 gigabytes in size, is named mirrorlv, and is carved out of volume group vg0: 
# lvcreate -L 50G -m1 -n mirrorlv vg0
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An LVM mirror divides the device being copied into regions that, by default, are 512KB in size. You can use the -R argument of the lvcreate command to specify the region size in megabytes. You can also change the default region size by editing the mirror_region_size setting in the lvm.conf file.

Note

Due to limitations in the cluster infrastructure, cluster mirrors greater than 1.5TB cannot be created with the default region size of 512KB. Users that require larger mirrors should increase the region size from its default to something larger. Failure to increase the region size will cause LVM creation to hang and may hang other LVM commands as well.
As a general guideline for specifying the region size for mirrors that are larger than 1.5TB, you could take your mirror size in terabytes and round up that number to the next power of 2, using that number as the -R argument to the lvcreate command. For example, if your mirror size is 1.5TB, you could specify -R 2. If your mirror size is 3TB, you could specify -R 4. For a mirror size of 5TB, you could specify -R 8.
The following command creates a mirrored logical volume with a region size of 2 MB: 
        # lvcreate -m1 -L 2T -R 2 -n mirror vol_group
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When a mirror is created, the mirror regions are synchronized. For large mirror components, the sync process may take a long time. When you are creating a new mirror that does not need to be revived, you can specify the --nosync argument to indicate that an initial synchronization from the first device is not required.
LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or mirrors. By default, this log is kept on disk, which keeps it persistent across reboots. You can specify instead that this log be kept in memory with the --corelog argument; this eliminates the need for an extra log device, but it requires that the entire mirror be resynchronized at every reboot.
The following command creates a mirrored logical volume from the volume group bigvg. The logical is named ondiskmirvol and has a single mirror. The volume is 12 MB in size and keeps the mirror log in memory. 
# lvcreate -L 12MB -m1 --corelog -n ondiskmirvol bigvg
  Logical volume "ondiskmirvol" created
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The mirror log is created on a separate device from the devices on which any of the mirror legs are created. It is possible, however, to create the mirror log on the same device as one of the mirror legs by using the --alloc anywhere argument of the vgcreate command. This may degrade performance, but it allows you to create a mirror even if you have only two underlying devices.
The following command creates a mirrored logical volume with a single mirror for which the mirror log is on the same device as one of the mirror legs. In this example, the volume group vg0 consists of only two devices. This command creates a 500 MB volume named mirrorlv in the vg0 volume group. 
# lvcreate -L 500M -m1 -n mirrorlv -alloc anywhere vg0
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Note

As of the Red Hat Enterprise Linux 5.7 release, you can combine RAID0 (striping) and RAID1 (mirroring) in a single logical volume. Creating a logical volume while simultaneously specifying the number of mirrors (--mirrors X) and the number of stripes (--stripes Y) results in a mirror device whose constituent devices are striped.

Note

With clustered mirrors, the mirror log management is completely the responsibility of the cluster node with the currently lowest cluster ID. Therefore, when the device holding the cluster mirror log becomes unavailable on a subset of the cluster, the clustered mirror can continue operating without any impact, as long as the cluster node with lowest ID retains access to the mirror log. Since the mirror is undisturbed, no automatic corrective action (repair) is issued, either. When the lowest-ID cluster node loses access to the mirror log, however, automatic action will kick in (regardless of accessibility of the log from other nodes).
5.4.1.3.1. Mirroring the Mirror Log
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To create a mirror log that is itself mirrored, you can specify the --mirrorlog mirrored argument. The following command creates a mirrored logical volume from the volume group bigvg. The logical volume is named twologvol and has a single mirror. The volume is 12 MB in size and the mirror log is mirrored, with each log kept on a separate device. 
# lvcreate -L 12MB -m1 --mirrorlog mirrored -n twologvol bigvg
  Logical volume "twologvol" created
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Just as with a standard mirror log, it is possible to create the redundant mirror logs on the same device as the mirror legs by using the --alloc anywhere argument of the vgcreate command. This may degrade performance, but it allows you to create a redundant mirror log even if you do not have sufficient underlying devices for each log to be kept on a separate device than the mirror legs.
You can specify which devices to use for the mirror legs and log, and which extents of the devices to use. To force the log onto a particular disk, specify exactly one extent on the disk on which it will be placed. LVM does not necessary respect the order in which devices are listed in the command line. If any physical volumes are listed that is the only space on which allocation will take place. Any physical extents included in the list that are already allocated will get ignored.
The following command creates a mirrored logical volume with a single mirror. The volume is 500 MB in size, it is named mirrorlv, and it is carved out of volume group vg0. The first leg of the mirror is on device /dev/sda1, the second leg of the mirror is on device /dev/sdb1, and the mirror log is on /dev/sdc1. 
# lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1 /dev/sdb1 /dev/sdc1
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The following command creates a mirrored logical volume with a single mirror. The volume is 500 MB in size, it is named mirrorlv, and it is carved out of volume group vg0. The first leg of the mirror is on extents 0 through 499 of device /dev/sda1, the second leg of the mirror is on extents 0 through 499 of device /dev/sdb1, and the mirror log starts on extent 0 of device /dev/sdc1. These are 1 MB extents. If any of the specified extents have already been allocated, they will be ignored. 
# lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1:0-499 /dev/sdb1:0-499 /dev/sdc1:0
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You can split off a redundant image of a mirrored logical volume to form a new logical volume. To split off an image, you use the --splitmirrors argument of the lvconvert command, specifying the number of redundant images to split off. You must use the --name argument of the command to specify a name for the newly-split-off logical volume.
The following command splits off a new logical volume named copy from the mirrored logical volume vg/lv. The new logical volume contains two mirror legs. In this example, LVM selects which devices to split off. 
# lvconvert --splitmirrors 2 --name copy vg/lv
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You can specify which devices to split off. The following command splits off a new logical volume named copy from the mirrored logical volume vg/lv. The new logical volume contains two mirror legs consisting of devices /dev/sdc1 and /dev/sde1. 
# lvconvert --splitmirrors 2 --name copy vg/lv /dev/sd[ce]1
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5.4.1.4. Changing Mirrored Volume Configuration
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You can convert a logical volume from a mirrored volume to a linear volume or from a linear volume to a mirrored volume with the lvconvert command. You can also use this command to reconfigure other mirror parameters of an existing logical volume, such as corelog.
When you convert a logical volume to a mirrored volume, you are basically creating mirror legs for an existing volume. This means that your volume group must contain the devices and space for the mirror legs and for the mirror log.
If you lose a leg of a mirror, LVM converts the volume to a linear volume so that you still have access to the volume, without the mirror redundancy. After you replace the leg, you can use the lvconvert command to restore the mirror. This procedure is provided in Section 7.3, “Recovering from LVM Mirror Failure”.
The following command converts the linear logical volume vg00/lvol1 to a mirrored logical volume. 
# lvconvert -m1 vg00/lvol1
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The following command converts the mirrored logical volume vg00/lvol1 to a linear logical volume, removing the mirror leg. 
# lvconvert -m0 vg00/lvol1
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5.4.2. Persistent Device Numbers
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Major and minor device numbers are allocated dynamically at module load. Some applications work best if the block device always is activated with the same device minor number. You can specify this with the lvcreate and the lvchange commands by using the following arguments: 
--persistent y --minor minor
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Use a large minor number to be sure that it has not already been allocated to another device dynamically.
If you are exporting a file system using NFS, specifying the fsid parameter in the exports file may avoid the need to set a persistent device number within LVM.

Note

Prior to the Red Hat Enterprise Linux 5.11 release, it was necessary to specify a major number when using the --persistent option. This had no effect on the major number, which the kernel assigned dynamically.

5.4.3. Resizing Logical Volumes
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To reduce the size of a logical volume, use the lvreduce command. If the logical volume contains a file system, be sure to reduce the file system first (or use the LVM GUI) so that the logical volume is always at least as large as the file system expects it to be.
The following command reduces the size of logical volume lvol1 in volume group vg00 by 3 logical extents. 
# lvreduce -l -3 vg00/lvol1
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To change the parameters of a logical volume, use the lvchange command. For a listing of the parameters you can change, see the lvchange(8) man page.
You can use the lvchange command to activate and deactivate logical volumes. To activate and deactivate all the logical volumes in a volume group at the same time, use the vgchange command, as described in Section 5.3.8, “Changing the Parameters of a Volume Group”.
The following command changes the permission on volume lvol1 in volume group vg00 to be read-only. 
# lvchange -pr vg00/lvol1
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5.4.5. Renaming Logical Volumes
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To rename an existing logical volume, use the lvrename command.
Either of the following commands renames logical volume lvold in volume group vg02 to lvnew. 
# lvrename /dev/vg02/lvold /dev/vg02/lvnew
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# lvrename vg02 lvold lvnew
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For more information on activating logical volumes on individual nodes in a cluster, see Section 5.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.

5.4.6. Removing Logical Volumes
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To remove an inactive logical volume, use the lvremove command. If the logical volume is currently mounted, unmount the volume before removing it. In addition, in a clustered environment you must deactivate a logical volume before it can be removed.
The following command removes the logical volume /dev/testvg/testlv. from the volume group testvg. Note that in this case the logical volume has not been deactivated. 
# lvremove /dev/testvg/testlv
Do you really want to remove active logical volume "testlv"? [y/n]: y
  Logical volume "testlv" successfully removed
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You could explicitly deactivate the logical volume before removing it with the lvchange -an command, in which case you would not see the prompt verifying whether you want to remove an active logical volume.

5.4.7. Displaying Logical Volumes
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There are three commands you can use to display properties of LVM logical volumes: lvs, lvdisplay, and lvscan.
The lvs command provides logical volume information in a configurable form, displaying one line per logical volume. The lvs command provides a great deal of format control, and is useful for scripting. For information on using the lvs command to customize your output, see Section 5.9, “Customized Reporting for LVM”.
The lvdisplay command displays logical volume properties (such as size, layout, and mapping) in a fixed format.
The following command shows the attributes of lvol2 in vg00. If snapshot logical volumes have been created for this original logical volume, this command shows a list of all snapshot logical volumes and their status (active or inactive) as well. 
# lvdisplay -v /dev/vg00/lvol2
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The lvscan command scans for all logical volumes in the system and lists them, as in the following example. 
# lvscan
 ACTIVE                   '/dev/vg0/gfslv' [1.46 GB] inherit
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5.4.8. Growing Logical Volumes
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To increase the size of a logical volume, use the lvextend command.
After extending the logical volume, you will need to increase the size of the associated file system to match.
When you extend the logical volume, you can indicate how much you want to extend the volume, or how large you want it to be after you extend it.
The following command extends the logical volume /dev/myvg/homevol to 12 gigabytes. 
# lvextend -L12G /dev/myvg/homevol 
lvextend -- extending logical volume "/dev/myvg/homevol" to 12 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
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The following command adds another gigabyte to the logical volume /dev/myvg/homevol. 
# lvextend -L+1G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 13 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
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As with the lvcreate command, you can use the -l argument of the lvextend command to specify the number of extents by which to increase the size of the logical volume. You can also use this argument to specify a percentage of the volume group, or a percentage of the remaining free space in the volume group. The following command extends the logical volume called testlv to fill all of the unallocated space in the volume group myvg. 
# lvextend -l +100%FREE /dev/myvg/testlv
  Extending logical volume testlv to 68.59 GB
  Logical volume testlv successfully resized
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After you have extended the logical volume it is necessary to increase the file system size to match.
By default, most file system resizing tools will increase the size of the file system to be the size of the underlying logical volume so you do not need to worry about specifying the same size for each of the two commands.

5.4.9. Extending a Striped Volume
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In order to increase the size of a striped logical volume, there must be enough free space on the underlying physical volumes that make up the volume group to support the stripe. For example, if you have a two-way stripe that that uses up an entire volume group, adding a single physical volume to the volume group will not enable you to extend the stripe. Instead, you must add at least two physical volumes to the volume group.
For example, consider a volume group vg that consists of two underlying physical volumes, as displayed with the following vgs command. 
# vgs
  VG   #PV #LV #SN Attr   VSize   VFree
  vg     2   0   0 wz--n- 271.31G 271.31G
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You can create a stripe using the entire amount of space in the volume group. 
# lvcreate -n stripe1 -L 271.31G -i 2 vg
  Using default stripesize 64.00 KB
  Rounding up size to full physical extent 271.31 GB
  Logical volume "stripe1" created
# lvs -a -o +devices
  LV      VG   Attr   LSize   Origin Snap%  Move Log Copy%  Devices
  stripe1 vg   -wi-a- 271.31G                               /dev/sda1(0),/dev/sdb1(0)
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Note that the volume group now has no more free space. 
# vgs
  VG   #PV #LV #SN Attr   VSize   VFree
  vg     2   1   0 wz--n- 271.31G    0
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The following command adds another physical volume to the volume group, which then has 135G of additional space. 
# vgextend vg /dev/sdc1
  Volume group "vg" successfully extended
# vgs
  VG   #PV #LV #SN Attr   VSize   VFree
  vg     3   1   0 wz--n- 406.97G 135.66G
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At this point you cannot extend the striped logical volume to the full size of the volume group, because two underlying devices are needed in order to stripe the data. 
# lvextend vg/stripe1 -L 406G
  Using stripesize of last segment 64.00 KB
  Extending logical volume stripe1 to 406.00 GB
  Insufficient suitable allocatable extents for logical volume stripe1: 34480 
more required
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To extend the striped logical volume, add another physical volume and then extend the logical volume. In this example, having added two physical volumes to the volume group we can extend the logical volume to the full size of the volume group. 
# vgextend vg /dev/sdd1
  Volume group "vg" successfully extended
# vgs
  VG   #PV #LV #SN Attr   VSize   VFree
  vg     4   1   0 wz--n- 542.62G 271.31G
# lvextend vg/stripe1 -L 542G
  Using stripesize of last segment 64.00 KB
  Extending logical volume stripe1 to 542.00 GB
  Logical volume stripe1 successfully resized
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If you do not have enough underlying physical devices to extend the striped logical volume, it is possible to extend the volume anyway if it does not matter that the extension is not striped, which may result in uneven performance. When adding space to the logical volume, the default operation is to use the same striping parameters of the last segment of the existing logical volume, but you can override those parameters. The following example extends the existing striped logical volume to use the remaining free space after the initial lvextend command fails. 
# lvextend vg/stripe1 -L 406G
  Using stripesize of last segment 64.00 KB
  Extending logical volume stripe1 to 406.00 GB
  Insufficient suitable allocatable extents for logical volume stripe1: 34480 
more required
# lvextend -i1 -l+100%FREE vg/stripe1
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5.4.10. Extending a Mirrored Volume
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As of the Red Hat Enterprise Linux 5.8 release, it is possible to grow mirrored logical volumes with the lvextend command without performing a synchronization of the new mirror regions.
If you specify the --nosync option when you create a mirrored logical volume with the lvcreate command, the mirror regions are not synchronized when the mirror is created, as described in Section 5.4.1.3, “Creating Mirrored Volumes”. If you later extend a mirror that you have created with the --nosync option, the mirror extensions are not synchronized at that time, either.
You can determine whether an existing logical volume was created with the --nosync option by using the lvs command to display the volume's attributes. A logical volume will have an attribute of "M" if it is a mirrored volume that was created without an initial synchronization, and it will have an attribute of "m" if it was created with initial synchronization.
The following command displays the attributes of a mirrored logical volume named lv that was created without initial synchronization. 
# lvs vg
  LV   VG   Attr     LSize Pool Origin Snap%  Move Log     Copy%  Convert
  lv   vg   Mwi-a-m- 5.00g                         lv_mlog 100.00
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If you grow this mirrored logical volume with the lvextend command, the mirror extension will not be resynchronized. For more information on displaying the attributes of logical volumes with the lvs command, refer to Table 5.3, “lvs Display Fields”.
If you created a mirrored logical volume without specifying the --nosync option of the lvcreate command, you can grow the logical volume without resynchronizing the mirror by specifying the --nosync option of the lvextend command.
The following example extends a logical volume that was created without the --nosync option, indicated that the mirror was synchronized when it was created. This example, however, specifies that the mirror not be synchronized when the volume is extended. Note that the volume has an attribute of "m", but after executing the lvextend commmand with the --nosync option the volume has an attribute of "M". 
# lvs vg
  LV   VG   Attr     LSize  Pool Origin Snap%  Move Log     Copy%  Convert
  lv   vg   mwi-a-m- 20.00m                         lv_mlog 100.00        
# lvextend -L +5G vg/lv --nosync
  Extending 2 mirror images.
  Extending logical volume lv to 5.02 GiB
  Logical volume lv successfully resized
# lvs vg
  LV   VG   Attr     LSize Pool Origin Snap%  Move Log     Copy%  Convert
  lv   vg   Mwi-a-m- 5.02g                         lv_mlog 100.00
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If a mirror is inactive, it will not automatically skip synchronization when you extend the mirror, even if you create the mirror with the --nosync option specified. Instead, you will be prompted whether to do a full resync of the extended portion of the logical volume.

Note

If a mirror is performing recovery, you cannot extend the mirrored logical volume if you created or extended the volume with the --nosync option specified. If you did not specify the --nosync option, however, you can extend the mirror while it is recovering.
As of the Red Hat Enterprise Linux 5.7 release, when extending an LVM volume, you can use the --alloc cling option of the lvextend command to specify the cling allocation policy. This policy will choose space on the same physical volumes as the last segment of the existing logical volume. If there is insufficient space on the physical volumes and a list of tags is defined in the lvm.conf file, LVM will check whether any of the tags are attached to the physical volumes and seek to match those physical volume tags between existing extents and new extents.
For example, if you have logical volumes that are mirrored between two sites within a single volume group, you can tag the physical volumes according to where they are situated by tagging the physical volumes with @site1 and @site2 tags and specify the following line in the lvm.conf file: 
cling_tag_list = [ "@site1", "@site2" ]
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For information on tagging physical volumes, see Appendix C, LVM Object Tags.
In the following example, the lvm.conf file has been modified to contain the following line: 
cling_tag_list = [ "@A", "@B" ]
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Also in this example, a volume group taft has been created that consists of the physical volumes /dev/sdb1, /dev/sdc1, /dev/sdd1, /dev/sde1, /dev/sdf1, /dev/sdg1, and /dev/sdh1. These physical volumes have been tagged with tags A, B, and C. The example does not use the C tag, but this will show that LVM uses the tags to select which physical volumes to use for the mirror legs. 
# pvs -a -o +pv_tags /dev/sd[bcdefgh]1
  PV         VG   Fmt  Attr PSize   PFree   PV Tags
  /dev/sdb1  taft lvm2 a-   135.66g 135.66g A
  /dev/sdc1  taft lvm2 a-   135.66g 135.66g B
  /dev/sdd1  taft lvm2 a-   135.66g 135.66g B
  /dev/sde1  taft lvm2 a-   135.66g 135.66g C
  /dev/sdf1  taft lvm2 a-   135.66g 135.66g C
  /dev/sdg1  taft lvm2 a-   135.66g 135.66g A
  /dev/sdh1  taft lvm2 a-   135.66g 135.66g A
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The following command creates a 100G mirrored volume from the volume group taft. 
# lvcreate -m 1 -n mirror --nosync -L 100G taft
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The following command shows which devices are used for the mirror legs and mirror log. 
# lvs -a -o +devices
  LV                VG        Attr   LSize   Log         Copy%  Devices
  mirror            taft      Mwi-a- 100.00g mirror_mlog 100.00
mirror_mimage_0(0),mirror_mimage_1(0)
  [mirror_mimage_0] taft      iwi-ao 100.00g                    /dev/sdb1(0)
  [mirror_mimage_1] taft      iwi-ao 100.00g                    /dev/sdc1(0)
  [mirror_mlog]     taft      lwi-ao   4.00m                    /dev/sdh1(0)
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The following command extends the size of the mirrored volume, using the cling allocation policy to indicate that the mirror legs should be extended using physical volumes with the same tag. 
# lvextend --alloc cling -L +100G taft/mirror
  Extending 2 mirror images.
  Extending logical volume mirror to 200.00 GiB
  Logical volume mirror successfully resized
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The following display command shows that the mirror legs have been extended using physical volumes with the same tag as the leg. Note that the physical volumes with a tag of C were ignored. 
# lvs -a -o +devices
  LV                VG        Attr   LSize   Log         Copy%  Devices
  mirror            taft      Mwi-a- 200.00g mirror_mlog  50.16
mirror_mimage_0(0),mirror_mimage_1(0)
  [mirror_mimage_0] taft      Iwi-ao 200.00g                    /dev/sdb1(0)
  [mirror_mimage_0] taft      Iwi-ao 200.00g                    /dev/sdg1(0)
  [mirror_mimage_1] taft      Iwi-ao 200.00g                    /dev/sdc1(0)
  [mirror_mimage_1] taft      Iwi-ao 200.00g                    /dev/sdd1(0)
  [mirror_mlog]     taft      lwi-ao   4.00m                    /dev/sdh1(0)
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5.4.12. Shrinking Logical Volumes
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To reduce the size of a logical volume, first unmount the file system. You can then use the lvreduce command to shrink the volume. After shrinking the volume, remount the file system.

Warning

It is important to reduce the size of the file system or whatever is residing in the volume before shrinking the volume itself, otherwise you risk losing data.
Shrinking a logical volume frees some of the volume group to be allocated to other logical volumes in the volume group.
The following example reduces the size of logical volume lvol1 in volume group vg00 by 3 logical extents. 
# lvreduce -l -3 vg00/lvol1
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5.5. Creating Snapshot Volumes
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Use the -s argument of the lvcreate command to create a snapshot volume. A snapshot volume is writable.

Note

LVM snapshots are not supported across the nodes in a cluster. You cannot create a snapshot volume in a clustered volume group. As of the Red Hat Enterprise Linux 5.7 release, however, if you need to create a consistent backup of data on a clustered logical volume that is not mirrored, you can activate the volume exclusively and then create the snapshot. For information on activating logical volumes exclusively on one node, see Section 5.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
The following command creates a snapshot logical volume that is 100 MB in size named /dev/vg00/snap. This creates a snapshot of the origin logical volume named /dev/vg00/lvol1. If the original logical volume contains a file system, you can mount the snapshot logical volume on an arbitrary directory in order to access the contents of the file system to run a backup while the original file system continues to get updated. 
# lvcreate --size 100M --snapshot --name snap /dev/vg00/lvol1
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After you create a snapshot logical volume, specifying the origin volume on the lvdisplay command yields output that includes a list of all snapshot logical volumes and their status (active or inactive).
The following example shows the status of the logical volume /dev/new_vg/lvol0, for which a snapshot volume /dev/new_vg/newvgsnap has been created. 
# lvdisplay /dev/new_vg/lvol0
  --- Logical volume ---
  LV Name                /dev/new_vg/lvol0
  VG Name                new_vg
  LV UUID                LBy1Tz-sr23-OjsI-LT03-nHLC-y8XW-EhCl78
  LV Write Access        read/write
  LV snapshot status     source of
                         /dev/new_vg/newvgsnap1 [active]
  LV Status              available
  # open                 0
  LV Size                52.00 MB
  Current LE             13
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:2
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The lvs command, by default, displays the origin volume and the current percentage of the snapshot volume being used for each snapshot volume. The following example shows the default output for the lvs command for a system that includes the logical volume /dev/new_vg/lvol0, for which a snapshot volume /dev/new_vg/newvgsnap has been created. 
# lvs
  LV         VG     Attr   LSize  Origin Snap%  Move Log Copy%
  lvol0      new_vg owi-a- 52.00M
  newvgsnap1 new_vg swi-a-  8.00M lvol0    0.20
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Warning

Because the snapshot increases in size as the origin volume changes, it is important to monitor the percentage of the snapshot volume regularly with the lvs command to be sure it does not fill. A snapshot that is 100% full is lost completely, as a write to unchanged parts of the origin would be unable to succeed without corrupting the snapshot.
As of the Red Hat Enterprise Linux 5.7 release, there are two new features related to snapshots. First, in addition to the snapshot itself being invalidated when full, any mounted file systems on that snapshot device are forcibly unmounted, avoiding the inevitable file system errors upon access to the mount point. Second, you can specify the snapshot_autoextend_threshold option in the lvm.conf file. This option allows automatic extension of a snapshot whenever the remaining snapshot space drops below the threshold you set. This feature requires that there be unallocated space in the volume group.
Information on setting snapshot_autoextend_threshold and snapshot_autoextend_percent is provided in the lvm.conf file itself. For information about the lvm.conf file, refer to Appendix B, The LVM Configuration Files.

5.6. Controlling LVM Device Scans with Filters
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At startup, the vgscan command is run to scan the block devices on the system looking for LVM labels, to determine which of them are physical volumes and to read the metadata and build up a list of volume groups. The names of the physical volumes are stored in the cache file of each node in the system, /etc/lvm/.cache. Subsequent commands may read that file to avoiding rescanning.
You can control which devices LVM scans by setting up filters in the lvm.conf configuration file. The filters in the lvm.conf file consist of a series of simple regular expressions that get applied to the device names that are in the /dev directory to decide whether to accept or reject each block device found.
The following examples show the use of filters to control which devices LVM scans. Note that some of these examples do not necessarily represent best practice, as the regular expressions are matched freely against the complete pathname. For example, a/loop/ is equivalent to a/.*loop.*/ and would match /dev/solooperation/lvol1.
The following filter adds all discovered devices, which is the default behavior as there is no filter configured in the configuration file: 
filter = [ "a/.*/" ]
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The following filter removes the cdrom device in order to avoid delays if the drive contains no media: 
filter = [ "r|/dev/cdrom|" ]
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The following filter adds all loop and removes all other block devices: 
filter = [ "a/loop.*/", "r/.*/" ]
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The following filter adds all loop and IDE and removes all other block devices: 
filter =[ "a|loop.*|", "a|/dev/hd.*|", "r|.*|" ]
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The following filter adds just partition 8 on the first IDE drive and removes all other block devices: 
filter = [ "a|^/dev/hda8$|", "r/.*/" ]
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For more information on the lvm.conf file, see Appendix B, The LVM Configuration Files and the lvm.conf(5) man page.

5.7. Online Data Relocation
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You can move data while the system is in use with the pvmove command.
The pvmove command breaks up the data to be moved into sections and creates a temporary mirror to move each section. For more information on the operation of the pvmove command, see the pvmove(8) man page.

Note

In order to perform a pvmove operation in a cluster, you should ensure that the cmirror and cmirror-kmod packages are installed and that the cmirror service is running. The cmirror-kmod package that must be installed depends on the kernel that is running. For example, if the running kernel is kernel-largesmp, it is necessary to have cmirror-kmod-largesmp for the corresponding kernel version.
The following command moves all allocated space off the physical volume /dev/sdc1 to other free physical volumes in the volume group: 
# pvmove /dev/sdc1
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The following command moves just the extents of the logical volume MyLV. 
# pvmove -n MyLV /dev/sdc1
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Since the pvmove command can take a long time to execute, you may want to run the command in the background to avoid display of progress updates in the foreground. The following command moves all extents allocated to the physical volume /dev/sdc1 over to /dev/sdf1 in the background. 
# pvmove -b /dev/sdc1 /dev/sdf1
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The following command reports the progress of the move as a percentage at five second intervals. 
# pvmove -i5 /dev/sdd1
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If you have LVM installed in a cluster environment, you may at times need to activate logical volumes exclusively on one node.
To activate logical volumes exclusively on one node, use the lvchange -aey command. Alternatively, you can use lvchange -aly command to activate logical volumes only on the local node but not exclusively. You can later activate them on additional nodes concurrently.
You can also activate logical volumes on individual nodes by using LVM tags, which are described in Appendix C, LVM Object Tags. You can also specify activation of nodes in the configuration file, which is described in Appendix B, The LVM Configuration Files.

5.9. Customized Reporting for LVM
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You can produce concise and customizable reports of LVM objects with the pvs, lvs, and vgs commands. The reports that these commands generate include one line of output for each object. Each line contains an ordered list of fields of properties related to the object. There are five ways to select the objects to be reported: by physical volume, volume group, logical volume, physical volume segment, and logical volume segment.
The following sections provide:
  • A summary of command arguments you can use to control the format of the generated report.
  • A list of the fields you can select for each LVM object.
  • A summary of command arguments you can use to sort the generated report.
  • Instructions for specifying the units of the report output.

5.9.1. Format Control
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Whether you use the pvs, lvs, or vgs command determines the default set of fields displayed and the sort order. You can control the output of these commands with the following arguments:
  • You can change what fields are displayed to something other than the default by using the -o argument. For example, the following output is the default display for the pvs command (which displays information about physcial volumes). 
    # pvs
  PV         VG     Fmt  Attr PSize  PFree
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.14G
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    The following command displays only the physical volume name and size. 
    # pvs -o pv_name,pv_size
  PV         PSize
  /dev/sdb1  17.14G
  /dev/sdc1  17.14G
  /dev/sdd1  17.14G
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  • You can append a field to the output with the plus sign (+), which is used in combination with the -o argument.
    The following example displays the UUID of the physical volume in addition to the default fields. 
    # pvs -o +pv_uuid
  PV         VG     Fmt  Attr PSize  PFree  PV UUID
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G Joqlch-yWSj-kuEn-IdwM-01S9-X08M-mcpsVe
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.14G yvfvZK-Cf31-j75k-dECm-0RZ3-0dGW-UqkCS
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  • Adding the -v argument to a command includes some extra fields. For example, the pvs -v command will display the DevSize and PV UUID fields in addition to the default fields. 
    # pvs -v
    Scanning for physical volume names
  PV         VG     Fmt  Attr PSize  PFree  DevSize PV UUID
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G  17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G  17.14G Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.14G  17.14G yvfvZK-Cf31-j75k-dECm-0RZ3-0dGW-tUqkCS
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  • The --noheadings argument suppresses the headings line. This can be useful for writing scripts.
    The following example uses the --noheadings argument in combination with the pv_name argument, which will generate a list of all physical volumes. 
    # pvs --noheadings -o pv_name
  /dev/sdb1
  /dev/sdc1
  /dev/sdd1
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  • The --separator separator argument uses separator to separate each field.
    The following example separates the default output fields of the pvs command with an equals sign (=). 
    # pvs --separator =
  PV=VG=Fmt=Attr=PSize=PFree
  /dev/sdb1=new_vg=lvm2=a-=17.14G=17.14G
  /dev/sdc1=new_vg=lvm2=a-=17.14G=17.09G
  /dev/sdd1=new_vg=lvm2=a-=17.14G=17.14G
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    To keep the fields aligned when using the separator argument, use the separator argument in conjunction with the --aligned argument. 
    # pvs --separator = --aligned
  PV        =VG    =Fmt =Attr=PSize =PFree
  /dev/sdb1 =new_vg=lvm2=a-  =17.14G=17.14G
  /dev/sdc1 =new_vg=lvm2=a-  =17.14G=17.09G
  /dev/sdd1 =new_vg=lvm2=a-  =17.14G=17.14G
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You can use the -P argument of the lvs or vgs command to display information about a failed volume that would otherwise not appear in the output. For information on the output this argument yields, see Section 7.2, “Displaying Information on Failed Devices”.
For a full listing of display arguments, see the pvs(8), vgs(8) and lvs(8) man pages.
Volume group fields can be mixed with either physical volume (and physical volume segment) fields or with logical volume (and logical volume segment) fields, but physical volume and logical volume fields cannot be mixed. For example, the following command will display one line of output for each physical volume. 
# vgs -o +pv_name
  VG     #PV #LV #SN Attr   VSize  VFree  PV
  new_vg   3   1   0 wz--n- 51.42G 51.37G /dev/sdc1
  new_vg   3   1   0 wz--n- 51.42G 51.37G /dev/sdd1
  new_vg   3   1   0 wz--n- 51.42G 51.37G /dev/sdb1
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5.9.2. Object Selection
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This section provides a series of tables that list the information you can display about the LVM objects with the pvs, vgs, and lvs commands.
For convenience, a field name prefix can be dropped if it matches the default for the command. For example, with the pvs command, name means pv_name, but with the vgs command, name is interpreted as vg_name.
Executing the following command is the equivalent of executing pvs -o pv_free. 
# pvs -o +free
  PFree
  17.14G
  17.09G
  17.14G
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The pvs Command
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Table 5.1, “pvs Display Fields” lists the display arguments of the pvs command, along with the field name as it appears in the header display and a description of the field.
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Table 5.1. pvs Display Fields
ArgumentHeaderDescription
dev_sizeDevSize The size of the underlying device on which the physical volume was created
pe_start1st PE Offset to the start of the first physical extent in the underlying device
pv_attrAttr Status of the physical volume: (a)llocatable or e(x)ported.
pv_fmtFmt The metadata format of the physical volume (lvm2 or lvm1)
pv_freePFree The free space remaining on the physical volume
pv_namePV The physical volume name
pv_pe_alloc_countAlloc Number of used physical extents
pv_pe_countPE Number of physical extents
pvseg_sizeSSize The segment size of the physical volume
pvseg_startStart The starting physical extent of the physical volume segment
pv_sizePSize The size of the physical volume
pv_tagsPV Tags LVM tags attached to the physical volume
pv_usedUsed The amount of space currently used on the physical volume
pv_uuidPV UUID The UUID of the physical volume
The pvs command displays the following fields by default: pv_name, vg_name, pv_fmt, pv_attr, pv_size, pv_free. The display is sorted by pv_name. 
# pvs
  PV         VG     Fmt  Attr PSize  PFree
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.13G
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Using the -v argument with the pvs command adds the following fields to the default display: dev_size, pv_uuid. 
# pvs -v
    Scanning for physical volume names
  PV         VG     Fmt  Attr PSize  PFree  DevSize PV UUID
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G  17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G  17.14G Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.13G  17.14G yvfvZK-Cf31-j75k-dECm-0RZ3-0dGW-tUqkCS
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You can use the --segments argument of the pvs command to display information about each physical volume segment. A segment is a group of extents. A segment view can be useful if you want to see whether your logical volume is fragmented.
The pvs --segments command displays the following fields by default: pv_name, vg_name, pv_fmt, pv_attr, pv_size, pv_free, pvseg_start, pvseg_size. The display is sorted by pv_name and pvseg_size within the physical volume. 
# pvs --segments
  PV         VG         Fmt  Attr PSize  PFree  Start SSize
  /dev/hda2  VolGroup00 lvm2 a-   37.16G 32.00M     0  1172
  /dev/hda2  VolGroup00 lvm2 a-   37.16G 32.00M  1172    16
  /dev/hda2  VolGroup00 lvm2 a-   37.16G 32.00M  1188     1
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G     0    26
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G    26    24
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G    50    26
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G    76    24
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G   100    26
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G   126    24
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G   150    22
  /dev/sda1  vg         lvm2 a-   17.14G 16.75G   172  4217
  /dev/sdb1  vg         lvm2 a-   17.14G 17.14G     0  4389
  /dev/sdc1  vg         lvm2 a-   17.14G 17.14G     0  4389
  /dev/sdd1  vg         lvm2 a-   17.14G 17.14G     0  4389
  /dev/sde1  vg         lvm2 a-   17.14G 17.14G     0  4389
  /dev/sdf1  vg         lvm2 a-   17.14G 17.14G     0  4389
  /dev/sdg1  vg         lvm2 a-   17.14G 17.14G     0  4389
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You can use the pvs -a command to see devices detected by LVM that have not been initialized as LVM physical volumes. 
# pvs -a
  PV                             VG     Fmt  Attr PSize  PFree
  /dev/VolGroup00/LogVol01                   --       0      0
  /dev/new_vg/lvol0                          --       0      0
  /dev/ram                                   --       0      0
  /dev/ram0                                  --       0      0
  /dev/ram2                                  --       0      0
  /dev/ram3                                  --       0      0
  /dev/ram4                                  --       0      0
  /dev/ram5                                  --       0      0
  /dev/ram6                                  --       0      0
  /dev/root                                  --       0      0
  /dev/sda                                   --       0      0
  /dev/sdb                                   --       0      0
  /dev/sdb1                      new_vg lvm2 a-   17.14G 17.14G
  /dev/sdc                                   --       0      0
  /dev/sdc1                      new_vg lvm2 a-   17.14G 17.09G
  /dev/sdd                                   --       0      0
  /dev/sdd1                      new_vg lvm2 a-   17.14G 17.14G
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The vgs Command
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Table 5.2, “vgs Display Fields” lists the display arguments of the vgs command, along with the field name as it appears in the header display and a description of the field.
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Table 5.2. vgs Display Fields
ArgumentHeaderDescription
lv_count#LV The number of logical volumes the volume group contains
max_lvMaxLV The maximum number of logical volumes allowed in the volume group (0 if unlimited)
max_pvMaxPV The maximum number of physical volumes allowed in the volume group (0 if unlimited)
pv_count#PV The number of physical volumes that define the volume group
snap_count#SN The number of snapshots the volume group contains
vg_attrAttr Status of the volume group: (w)riteable, (r)eadonly, resi(z)eable, e(x)ported, (p)artial and (c)lustered.
vg_extent_count#Ext The number of physical extents in the volume group
vg_extent_sizeExt The size of the physical extents in the volume group
vg_fmtFmt The metadata format of the volume group (lvm2 or lvm1)
vg_freeVFree Size of the free space remaining in the volume group
vg_free_countFree Number of free physical extents in the volume group
vg_nameVG The volume group name
vg_seqnoSeq Number representing the revision of the volume group
vg_sizeVSize The size of the volume group
vg_sysidSYS ID LVM1 System ID
vg_tagsVG Tags LVM tags attached to the volume group
vg_uuidVG UUID The UUID of the volume group
The vgs command displays the following fields by default: vg_name, pv_count, lv_count, snap_count, vg_attr, vg_size, vg_free. The display is sorted by vg_name. 
# vgs
  VG     #PV #LV #SN Attr   VSize  VFree
  new_vg   3   1   1 wz--n- 51.42G 51.36G
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Using the -v argument with the vgs command adds the following fields to the default display: vg_extent_size, vg_uuid. 
# vgs -v
    Finding all volume groups
    Finding volume group "new_vg"
  VG     Attr   Ext   #PV #LV #SN VSize  VFree  VG UUID
  new_vg wz--n- 4.00M   3   1   1 51.42G 51.36G jxQJ0a-ZKk0-OpMO-0118-nlwO-wwqd-fD5D32
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The lvs Command
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Table 5.3, “lvs Display Fields” lists the display arguments of the lvs command, along with the field name as it appears in the header display and a description of the field.
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Table 5.3. lvs Display Fields
ArgumentHeaderDescription
chunksize
chunk_size
Chunk Unit size in a snapshot volume
copy_percentCopy% The synchronization percentage of a mirrored logical volume; also used when physical extents are being moved with the pv_move command
devicesDevices The underlying devices that make up the logical volume: the physical volumes, logical volumes, and start physical extents and logical extents
lv_attrAttr The status of the logical volume. The logical volume attribute bits are as follows:
Bit 1: Volume type: (m)irrored, (M)irrored without initial sync, (o)rigin, (p)vmove, (s)napshot, invalid (S)napshot, (v)irtual
Bit2: Permissions: (w)riteable, (r)ead-only
Bit 3: Allocation policy: (c)ontiguous, (n)ormal, (a)nywhere, (i)nherited. This is capitalized if the volume is currently locked against allocation changes, for example while executing the pvmove command.
Bit 4: fixed (m)inor
Bit 5 State: (a)ctive, (s)uspended, (I)nvalid snapshot, invalid (S)uspended snapshot, mapped (d)evice present without tables, mapped device present with (i)nactive table
Bit 6: device (o)pen
lv_kernel_majorKMaj Actual major device number of the logical volume (-1 if inactive)
lv_kernel_minorKMIN Actual minor device number of the logical volume (-1 if inactive)
lv_majorMaj The persistent major device number of the logical volume (-1 if not specified)
lv_minorMin The persistent minor device number of the logical volume (-1 if not specified)
lv_nameLV The name of the logical volume
lv_sizeLSize The size of the logical volume
lv_tagsLV Tags LVM tags attached to the logical volume
lv_uuidLV UUID The UUID of the logical volume.
mirror_logLog Device on which the mirror log resides
modulesModules Corresponding kernel device-mapper target necessary to use this logical volume
move_pvMove Source physical volume of a temporary logical volume created with the pvmove command
originOrigin The origin device of a snapshot volume
regionsize
region_size
Region The unit size of a mirrored logical volume
seg_count#Seg The number of segments in the logical volume
seg_sizeSSize The size of the segments in the logical volume
seg_startStart Offset of the segment in the logical volume
seg_tagsSeg Tags LVM tags attached to the segments of the logical volume
segtypeType The segment type of a logical volume (for example: mirror, striped, linear)
snap_percentSnap% Current percentage of a snapshot volume that is in use
stripes#Str Number of stripes or mirrors in a logical volume
stripesize
stripe_size
Stripe Unit size of the stripe in a striped logical volume
The lvs command displays the following fields by default: lv_name, vg_name, lv_attr, lv_size, origin, snap_percent, move_pv, mirror_log, copy_percent, convert_lv. The default display is sorted by vg_name and lv_name within the volume group. 
# lvs
  LV         VG     Attr   LSize  Origin Snap%  Move Log Copy%  Convert
  lvol0      new_vg owi-a- 52.00M
  newvgsnap1 new_vg swi-a-  8.00M lvol0    0.20
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Using the -v argument with the lvs command adds the following fields to the default display: seg_count, lv_major, lv_minor, lv_kernel_major, lv_kernel_minor, lv_uuid. 
# lvs -v
    Finding all logical volumes
  LV         VG     #Seg Attr   LSize  Maj Min KMaj KMin Origin Snap%  Move Copy%  Log Convert LV UUID
  lvol0      new_vg    1 owi-a- 52.00M  -1  -1 253  3                                          LBy1Tz-sr23-OjsI-LT03-nHLC-y8XW-EhCl78
  newvgsnap1 new_vg    1 swi-a-  8.00M  -1  -1 253  5    lvol0    0.20                         1ye1OU-1cIu-o79k-20h2-ZGF0-qCJm-CfbsIx
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You can use the --segments argument of the lvs command to display information with default columns that emphasize the segment information. When you use the segments argument, the seg prefix is optional. The lvs --segments command displays the following fields by default: lv_name, vg_name, lv_attr, stripes, segtype, seg_size. The default display is sorted by vg_name, lv_name within the volume group, and seg_start within the logical volume. If the logical volumes were fragmented, the output from this command would show that. 
# lvs --segments
  LV       VG         Attr   #Str Type   SSize
  LogVol00 VolGroup00 -wi-ao    1 linear  36.62G
  LogVol01 VolGroup00 -wi-ao    1 linear 512.00M
  lv       vg         -wi-a-    1 linear 104.00M
  lv       vg         -wi-a-    1 linear 104.00M
  lv       vg         -wi-a-    1 linear 104.00M
  lv       vg         -wi-a-    1 linear  88.00M
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Using the -v argument with the lvs --segments command adds the following fields to the default display: seg_start, stripesize, chunksize. 
# lvs -v --segments
    Finding all logical volumes
  LV         VG     Attr   Start SSize  #Str Type   Stripe Chunk
  lvol0      new_vg owi-a-    0  52.00M    1 linear     0     0
  newvgsnap1 new_vg swi-a-    0   8.00M    1 linear     0  8.00K
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The following example shows the default output of the lvs command on a system with one logical volume configured, followed by the default output of the lvs command with the segments argument specified. 
# lvs
  LV    VG     Attr   LSize  Origin Snap%  Move Log Copy%
  lvol0 new_vg -wi-a- 52.00M
# lvs --segments
  LV    VG     Attr   #Str Type   SSize
  lvol0 new_vg -wi-a-    1 linear 52.00M
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5.9.3. Sorting LVM Reports
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Normally the entire output of the lvs, vgs, or pvs command has to be generated and stored internally before it can be sorted and columns aligned correctly. You can specify the --unbuffered argument to display unsorted output as soon as it is generated.
To specify an alternative ordered list of columns to sort on, use the -O argument of any of the reporting commands. It is not necessary to include these fields within the output itself.
The following example shows the output of the pvs command that displays the physical volume name, size, and free space. 
# pvs -o pv_name,pv_size,pv_free
  PV         PSize  PFree
  /dev/sdb1  17.14G 17.14G
  /dev/sdc1  17.14G 17.09G
  /dev/sdd1  17.14G 17.14G
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The following example shows the same output, sorted by the free space field. 
# pvs -o pv_name,pv_size,pv_free -O pv_free
  PV         PSize  PFree
  /dev/sdc1  17.14G 17.09G
  /dev/sdd1  17.14G 17.14G
  /dev/sdb1  17.14G 17.14G
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The following example shows that you do not need to display the field on which you are sorting. 
# pvs -o pv_name,pv_size -O pv_free
  PV         PSize
  /dev/sdc1  17.14G
  /dev/sdd1  17.14G
  /dev/sdb1  17.14G
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To display a reverse sort, precede a field you specify after the -O argument with the - character. 
# pvs -o pv_name,pv_size,pv_free -O -pv_free
  PV         PSize  PFree
  /dev/sdd1  17.14G 17.14G
  /dev/sdb1  17.14G 17.14G
  /dev/sdc1  17.14G 17.09G
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5.9.4. Specifying Units
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To specify the unit for the LVM report display, use the --units argument of the report command. You can specify (b)ytes, (k)ilobytes, (m)egabytes, (g)igabytes, (t)erabytes, (e)xabytes, (p)etabytes, and (h)uman-readable. The default display is human-readable. You can override the default by setting the units parameter in the global section of the lvm.conf file.
The following example specifies the output of the pvs command in megabytes rather than the default gigabytes. 
# pvs --units m
  PV         VG     Fmt  Attr PSize     PFree
  /dev/sda1         lvm2 --   17555.40M 17555.40M
  /dev/sdb1  new_vg lvm2 a-   17552.00M 17552.00M
  /dev/sdc1  new_vg lvm2 a-   17552.00M 17500.00M
  /dev/sdd1  new_vg lvm2 a-   17552.00M 17552.00M
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By default, units are displayed in powers of 2 (multiples of 1024). You can specify that units be displayed in multiples of 1000 by capitalizing the unit specification (B, K, M, G, T, H).
The following command displays the output as a multiple of 1024, the default behavior. 
# pvs
  PV         VG     Fmt  Attr PSize  PFree
  /dev/sdb1  new_vg lvm2 a-   17.14G 17.14G
  /dev/sdc1  new_vg lvm2 a-   17.14G 17.09G
  /dev/sdd1  new_vg lvm2 a-   17.14G 17.14G
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The following command displays the output as a multiple of 1000. 
#  pvs --units G
  PV         VG     Fmt  Attr PSize  PFree
  /dev/sdb1  new_vg lvm2 a-   18.40G 18.40G
  /dev/sdc1  new_vg lvm2 a-   18.40G 18.35G
  /dev/sdd1  new_vg lvm2 a-   18.40G 18.40G
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You can also specify (s)ectors (defined as 512 bytes) or custom units.
The following example displays the output of the pvs command as a number of sectors. 
# pvs --units s
  PV         VG     Fmt  Attr PSize     PFree
  /dev/sdb1  new_vg lvm2 a-   35946496S 35946496S
  /dev/sdc1  new_vg lvm2 a-   35946496S 35840000S
  /dev/sdd1  new_vg lvm2 a-   35946496S 35946496S
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The following example displays the output of the pvs command in units of 4 megabytes. 
# pvs --units 4m
  PV         VG     Fmt  Attr PSize    PFree
  /dev/sdb1  new_vg lvm2 a-   4388.00U 4388.00U
  /dev/sdc1  new_vg lvm2 a-   4388.00U 4375.00U
  /dev/sdd1  new_vg lvm2 a-   4388.00U 4388.00U
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Chapter 6. LVM Configuration Examples
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This chapter provides some basic LVM configuration examples.

6.1. Creating an LVM Logical Volume on Three Disks
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This example creates an LVM logical volume called new_logical_volume that consists of the disks at /dev/sda1, /dev/sdb1, and /dev/sdc1.

6.1.1. Creating the Physical Volumes
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To use disks in a volume group, you label them as LVM physical volumes.

Warning

This command destroys any data on /dev/sda1, /dev/sdb1, and /dev/sdc1. 
# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1
  Physical volume "/dev/sda1" successfully created
  Physical volume "/dev/sdb1" successfully created
  Physical volume "/dev/sdc1" successfully created
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6.1.2. Creating the Volume Group
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The following command creates the volume group new_vol_group. 
# vgcreate new_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1
  Volume group "new_vol_group" successfully created
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You can use the vgs command to display the attributes of the new volume group. 
# vgs
  VG            #PV #LV #SN Attr   VSize  VFree
  new_vol_group   3   0   0 wz--n- 51.45G 51.45G
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6.1.3. Creating the Logical Volume
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The following command creates the logical volume new_logical_volume from the volume group new_vol_group. This example creates a logical volume that uses 2GB of the volume group. 
# lvcreate -L2G -n new_logical_volume new_vol_group
  Logical volume "new_logical_volume" created
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6.1.4. Creating the File System
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The following command creates a GFS file system on the logical volume. 
# gfs_mkfs -plock_nolock -j 1 /dev/new_vol_group/new_logical_volume
This will destroy any data on /dev/new_vol_group/new_logical_volume.

Are you sure you want to proceed? [y/n] y

Device:                    /dev/new_vol_group/new_logical_volume
Blocksize:                 4096
Filesystem Size:           491460
Journals:                  1
Resource Groups:           8
Locking Protocol:          lock_nolock
Lock Table:

Syncing...
All Done
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The following commands mount the logical volume and report the file system disk space usage. 
# mount /dev/new_vol_group/new_logical_volume /mnt
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/new_vol_group/new_logical_volume
                       1965840        20   1965820   1% /mnt
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6.2. Creating a Striped Logical Volume
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This example creates an LVM striped logical volume called striped_logical_volume that stripes data across the disks at /dev/sda1, /dev/sdb1, and /dev/sdc1.

6.2.1. Creating the Physical Volumes
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Label the disks you will use in the volume groups as LVM physical volumes.

Warning

This command destroys any data on /dev/sda1, /dev/sdb1, and /dev/sdc1. 
# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1
  Physical volume "/dev/sda1" successfully created
  Physical volume "/dev/sdb1" successfully created
  Physical volume "/dev/sdc1" successfully created
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6.2.2. Creating the Volume Group
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The following command creates the volume group volgroup01. 
# vgcreate volgroup01 /dev/sda1 /dev/sdb1 /dev/sdc1
  Volume group "volgroup01" successfully created
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You can use the vgs command to display the attributes of the new volume group. 
# vgs
  VG                #PV #LV #SN Attr   VSize  VFree
  volgroup01          3   0   0 wz--n- 51.45G 51.45G
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6.2.3. Creating the Logical Volume
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The following command creates the striped logical volume striped_logical_volume from the volume group volgroup01. This example creates a logical volume that is 2 gigabytes in size, with three stripes and a stripe size of 4 kilobytes. 
# lvcreate -i3 -I4 -L2G -nstriped_logical_volume volgroup01
  Rounding size (512 extents) up to stripe boundary size (513 extents)
  Logical volume "striped_logical_volume" created
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6.2.4. Creating the File System
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The following command creates a GFS file system on the logical volume. 
#  gfs_mkfs -plock_nolock -j 1 /dev/volgroup01/striped_logical_volume
This will destroy any data on /dev/volgroup01/striped_logical_volume.

Are you sure you want to proceed? [y/n] y

Device:                    /dev/volgroup01/striped_logical_volume
Blocksize:                 4096
Filesystem Size:           492484
Journals:                  1
Resource Groups:           8
Locking Protocol:          lock_nolock
Lock Table:

Syncing...
All Done
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The following commands mount the logical volume and report the file system disk space usage. 
# mount /dev/volgroup01/striped_logical_volume /mnt
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      13902624   1656776  11528232  13% /
/dev/hda1               101086     10787     85080  12% /boot
tmpfs                   127880         0    127880   0% /dev/shm
/dev/volgroup01/striped_logical_volume
                       1969936        20   1969916   1% /mnt
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6.3. Splitting a Volume Group
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In this example, an existing volume group consists of three physical volumes. If there is enough unused space on the physical volumes, a new volume group can be created without adding new disks.
In the initial set up, the logical volume mylv is carved from the volume group myvol, which in turn consists of the three physical volumes, /dev/sda1, /dev/sdb1, and /dev/sdc1.
After completing this procedure, the volume group myvg will consist of /dev/sda1 and /dev/sdb1. A second volume group, yourvg, will consist of /dev/sdc1.

6.3.1. Determining Free Space
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You can use the pvscan command to determine how much free space is currently available in the volume group. 
# pvscan
  PV /dev/sda1   VG myvg   lvm2 [17.15 GB / 0    free]
  PV /dev/sdb1   VG myvg   lvm2 [17.15 GB / 12.15 GB free]
  PV /dev/sdc1  VG myvg   lvm2 [17.15 GB / 15.80 GB free]
  Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0   ]
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6.3.2. Moving the Data
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You can move all the used physical extents in /dev/sdc1 to /dev/sdb1 with the pvmove command. The pvmove command can take a long time to execute. 
# pvmove /dev/sdc1 /dev/sdb1
  /dev/sdc1: Moved: 14.7%
  /dev/sdc1: Moved: 30.3%
  /dev/sdc1: Moved: 45.7%
  /dev/sdc1: Moved: 61.0%
  /dev/sdc1: Moved: 76.6%
  /dev/sdc1: Moved: 92.2%
  /dev/sdc1: Moved: 100.0%
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After moving the data, you can see that all of the space on /dev/sdc1 is free. 
# pvscan
  PV /dev/sda1   VG myvg   lvm2 [17.15 GB / 0    free]
  PV /dev/sdb1   VG myvg   lvm2 [17.15 GB / 10.80 GB free]
  PV /dev/sdc1   VG myvg   lvm2 [17.15 GB / 17.15 GB free]
  Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0   ]
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6.3.3. Splitting the Volume Group
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To create the new volume group yourvg, use the vgsplit command to split the volume group myvg.
Before you can split the volume group, the logical volume must be inactive. If the file system is mounted, you must unmount the file system before deactivating the logical volume.
You can deactivate the logical volumes with the lvchange command or the vgchange command. The following command deactivates the logical volume mylv and then splits the volume group yourvg from the volume group myvg, moving the physical volume /dev/sdc1 into the new volume group yourvg. 
# lvchange -a n /dev/myvg/mylv
# vgsplit myvg yourvg /dev/sdc1
  Volume group "yourvg" successfully split from "myvg"
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You can use the vgs command to see the attributes of the two volume groups. 
# vgs
  VG     #PV #LV #SN Attr   VSize  VFree
  myvg     2   1   0 wz--n- 34.30G 10.80G
  yourvg   1   0   0 wz--n- 17.15G 17.15G
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6.3.4. Creating the New Logical Volume
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After creating the new volume group, you can create the new logical volume yourlv. 
# lvcreate -L5G -n yourlv yourvg
  Logical volume "yourlv" created
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You can make a file system on the new logical volume and mount it. 
#  gfs_mkfs -plock_nolock -j 1 /dev/yourvg/yourlv
This will destroy any data on /dev/yourvg/yourlv.

Are you sure you want to proceed? [y/n] y

Device:                    /dev/yourvg/yourlv
Blocksize:                 4096
Filesystem Size:           1277816
Journals:                  1
Resource Groups:           20
Locking Protocol:          lock_nolock
Lock Table:

Syncing...
All Done

# mount /dev/yourvg/yourlv /mnt
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Since you had to deactivate the logical volume mylv, you need to activate it again before you can mount it. 
# lvchange -a y /dev/myvg/mylv

# mount /dev/myvg/mylv /mnt
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/yourvg/yourlv    24507776        32  24507744   1% /mnt
/dev/myvg/mylv        24507776        32  24507744   1% /mnt
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6.4. Removing a Disk from a Logical Volume
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This example shows how you can remove a disk from an existing logical volume, either to replace the disk or to use the disk as part of a different volume. In order to remove a disk, you must first move the extents on the LVM physical volume to a different disk or set of disks.

6.4.1. Moving Extents to Existing Physical Volumes
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In this example, the logical volume is distributed across four physical volumes in the volume group myvg. 
# pvs -o+pv_used
  PV         VG   Fmt  Attr PSize  PFree  Used
  /dev/sda1  myvg lvm2 a-   17.15G 12.15G  5.00G
  /dev/sdb1  myvg lvm2 a-   17.15G 12.15G  5.00G
  /dev/sdc1  myvg lvm2 a-   17.15G 12.15G  5.00G
  /dev/sdd1  myvg lvm2 a-   17.15G  2.15G 15.00G
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We want to move the extents off of /dev/sdb1 so that we can remove it from the volume group.
If there are enough free extents on the other physical volumes in the volume group, you can execute the pvmove command on the device you want to remove with no other options and the extents will be distributed to the other devices. 
# pvmove /dev/sdb1
  /dev/sdb1: Moved: 2.0%
 ...
  /dev/sdb1: Moved: 79.2%
 ...
  /dev/sdb1: Moved: 100.0%
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After the pvmove command has finished executing, the distribution of extents is as follows: 
# pvs -o+pv_used
  PV         VG   Fmt  Attr PSize  PFree  Used
  /dev/sda1  myvg lvm2 a-   17.15G  7.15G 10.00G
  /dev/sdb1  myvg lvm2 a-   17.15G 17.15G     0
  /dev/sdc1  myvg lvm2 a-   17.15G 12.15G  5.00G
  /dev/sdd1  myvg lvm2 a-   17.15G  2.15G 15.00G
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Use the vgreduce command to remove the physical volume /dev/sdb1 from the volume group. 
# vgreduce myvg /dev/sdb1
  Removed "/dev/sdb1" from volume group "myvg"
# pvs
  PV         VG   Fmt  Attr PSize  PFree
  /dev/sda1  myvg lvm2 a-   17.15G  7.15G
  /dev/sdb1       lvm2 --   17.15G 17.15G
  /dev/sdc1  myvg lvm2 a-   17.15G 12.15G
  /dev/sdd1  myvg lvm2 a-   17.15G  2.15G
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The disk can now be physically removed or allocated to other users.

6.4.2. Moving Extents to a New Disk
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In this example, the logical volume is distributed across three physical volumes in the volume group myvg as follows: 
# pvs -o+pv_used
  PV         VG   Fmt  Attr PSize  PFree  Used
  /dev/sda1  myvg lvm2 a-   17.15G  7.15G 10.00G
  /dev/sdb1  myvg lvm2 a-   17.15G 15.15G  2.00G
  /dev/sdc1  myvg lvm2 a-   17.15G 15.15G  2.00G
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We want to move the extents of /dev/sdb1 to a new device, /dev/sdd1.
6.4.2.1. Creating the New Physical Volume
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Create a new physical volume from /dev/sdd1. 
# pvcreate /dev/sdd1
  Physical volume "/dev/sdd1" successfully created
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Add /dev/sdd1 to the existing volume group myvg. 
# vgextend myvg /dev/sdd1
  Volume group "myvg" successfully extended
# pvs -o+pv_used
  PV         VG   Fmt  Attr PSize  PFree  Used
  /dev/sda1   myvg lvm2 a-   17.15G  7.15G 10.00G
  /dev/sdb1   myvg lvm2 a-   17.15G 15.15G  2.00G
  /dev/sdc1   myvg lvm2 a-   17.15G 15.15G  2.00G
  /dev/sdd1   myvg lvm2 a-   17.15G 17.15G     0
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6.4.2.3. Moving the Data
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Use the pvmove command to move the data from /dev/sdb1 to /dev/sdd1. 
# pvmove /dev/sdb1 /dev/sdd1
  /dev/sdb1: Moved: 10.0%
...
  /dev/sdb1: Moved: 79.7%
...
  /dev/sdb1: Moved: 100.0%

# pvs -o+pv_used
  PV          VG   Fmt  Attr PSize  PFree  Used
  /dev/sda1   myvg lvm2 a-   17.15G  7.15G 10.00G
  /dev/sdb1   myvg lvm2 a-   17.15G 17.15G     0
  /dev/sdc1   myvg lvm2 a-   17.15G 15.15G  2.00G
  /dev/sdd1   myvg lvm2 a-   17.15G 15.15G  2.00G
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After you have moved the data off /dev/sdb1, you can remove it from the volume group. 
# vgreduce myvg /dev/sdb1
  Removed "/dev/sdb1" from volume group "myvg"
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You can now reallocate the disk to another volume group or remove the disk from the system.
Creating a mirrored LVM logical volume in a cluster requires the same commands and procedures as creating a mirrored LVM logical volume on a single node. However, in order to create a mirrored LVM volume in a cluster the cluster and cluster mirror infrastructure must be running, the cluster must be quorate, and the locking type in the lvm.conf file must be set correctly to enable cluster locking, either directly or by means of the lvmconf command as described in Section 4.1, “Creating LVM Volumes in a Cluster”.
The following procedure creates a mirrored LVM volume in a cluster. First the procedure checks to see whether the cluster services are installed and running, then the procedure creates the mirrored volume.
  1. In order to create a mirrored logical volume that is shared by all of the nodes in a cluster, the locking type must be set correctly in the lvm.conf file in every node of the cluster. By default, the locking type is set to local. To change this, execute the following command in each node of the cluster to enable clustered locking: 
    # /usr/sbin/lvmconf --enable-cluster
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  2. To create a clustered logical volume, the cluster infrastructure must be up and running on every node in the cluster. The following example verifies that the clvmd daemon is running on the node from which it was issued: 
    # ps auxw | grep clvmd
root     17642  0.0  0.1 32164 1072 ?        Ssl  Apr06   0:00 clvmd -T20 -t 90
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    The following command shows the local view of the cluster status: 
    # cman_tool services
Service          Name                              GID LID State     Code
...
DLM Lock Space:  "clvmd"                             7   3 run       -
[1 2 3]
...
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  3. Ensure that the cmirror and cmirror-kmod packages are installed. The cmirror-kmod package that must be installed depends on the kernel that is running. For example, if the running kernel is kernel-largesmp, it is necessary to have cmirror-kmod-largesmp for the corresponding kernel version.
  4. Start the cmirror service. 
    # service cmirror start
Loading clustered mirror log:                              [  OK  ]
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  5. Create the mirror. The first step is creating the physical volumes. The following commands create three physical volumes. Two of the physical volumes will be used for the legs of the mirror, and the third physical volume will contain the mirror log. 
    # pvcreate /dev/xvdb1
  Physical volume "/dev/xvdb1" successfully created
# pvcreate /dev/xvdb2
  Physical volume "/dev/xvdb2" successfully created
# pvcreate /dev/xvdc1
  Physical volume "/dev/xvdc1" successfully created
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  6. Create the volume group. This example creates a volume group vg001 that consists of the three physical volumes that were created in the previous step. 
    # vgcreate vg001 /dev/xvdb1 /dev/xvdb2 /dev/xvdc1
  Clustered volume group "vg001" successfully created
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    Note that the output of the vgcreate command indicates that the volume group is clustered. You can verify that a volume group is clustered with the vgs command, which will show the volume group's attributes. If a volume group is clustered, it will show a c attribute. 
    # vgs vg001
  VG       #PV #LV #SN Attr   VSize  VFree
  vg001      3   0   0 wz--nc 68.97G 68.97G
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  7. Create the mirrored logical volume. This example creates the logical volume mirrorlv from the volume group vg001. This volume has one mirror leg. This example specifies which extents of the physical volume will be used for the logical volume. 
    # lvcreate -l 1000 -m1 vg001 -n mirrorlv /dev/xvdb1:1-1000 /dev/xvdb2:1-1000 /dev/xvdc1:0
  Logical volume "mirrorlv" created
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    You can use the lvs command to display the progress of the mirror creation. The following example shows that the mirror is 47% synced, then 91% synced, then 100% synced when the mirror is complete. 
    # lvs vg001/mirrorlv
  LV       VG       Attr   LSize Origin Snap%  Move Log           Copy%  Convert
  mirrorlv vg001    mwi-a- 3.91G                    vg001_mlog     47.00
# lvs vg001/mirrorlv
  LV       VG       Attr   LSize Origin Snap%  Move Log           Copy%  Convert
  mirrorlv vg001    mwi-a- 3.91G                    vg001_mlog     91.00   
#  lvs vg001/mirrorlv
  LV       VG       Attr   LSize Origin Snap%  Move Log           Copy%  Convert
  mirrorlv vg001    mwi-a- 3.91G                    vg001_mlog    100.00
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    The completion of the mirror is noted in the system log: 
    May 10 14:52:52 doc-07 [19402]: Monitoring mirror device vg001-mirrorlv for events
May 10 14:55:00 doc-07 lvm[19402]: vg001-mirrorlv is now in-sync
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  8. You can use the lvs with the -o +devices options to display the configuration of the mirror, including which devices make up the mirror legs. You can see that the logical volume in this example is composed of two linear images and one log. 
    # lvs -a -o +devices
  LV                  VG         Attr   LSize  Origin Snap%  Move Log           Copy%  Convert Devices                                  
  mirrorlv            vg001      mwi-a-  3.91G                    mirrorlv_mlog 100.00         mirrorlv_mimage_0(0),mirrorlv_mimage_1(0)
  [mirrorlv_mimage_0] vg001      iwi-ao  3.91G                                                 /dev/xvdb1(1)                            
  [mirrorlv_mimage_1] vg001      iwi-ao  3.91G                                                 /dev/xvdb2(1)                            
  [mirrorlv_mlog]     vg001      lwi-ao  4.00M                                                 /dev/xvdc1(0)
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    For Red Hat Enterprise Linux 5.2 and later, you can use the seg_pe_ranges option of the lvs to display the data layout. You can use this option to verify that your layout is properly redundant. The output of this command displays PE ranges in the same format that the lvcreate and lvresize commands take as input. 
    # lvs -a -o +seg_pe_ranges --segments
  PE Ranges                                      
  mirrorlv_mimage_0:0-999 mirrorlv_mimage_1:0-999
  /dev/xvdb1:1-1000                              
  /dev/xvdb2:1-1000                              
  /dev/xvdc1:0-0
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    When you create the mirrored volume, you create the clustered_log dlm space, which will contain the dlm locks for all mirrors. 
    # cman_tool services
Service          Name                              GID LID State     Code
Fence Domain:    "default"                           4   2 run       -
[1 2 3]

DLM Lock Space:  "clvmd"                            12   7 run       -
[1 2 3]

DLM Lock Space:  "clustered_log"                    14   9 run       -
[1 2 3]

User:            "usrm::manager"                    10   4 run       -
[1 2 3]
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Note

For information on recovering from the failure of one of the legs of an LVM mirrored volume, see Section 7.3, “Recovering from LVM Mirror Failure”.

Chapter 7. LVM Troubleshooting
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This chapter provide instructions for troubleshooting a variety of LVM issues.

7.1. Troubleshooting Diagnostics
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If a command is not working as expected, you can gather diagnostics in the following ways:
  • Use the -v, -vv, -vvv, or -vvvv argument of any command for increasingly verbose levels of output.
  • If the problem is related to the logical volume activation, set 'activation = 1' in the 'log' section of the configuration file and run the command with the -vvvv argument. After you have finished examining this output be sure to reset this parameter to 0, to avoid possible problems with the machine locking during low memory situations.
  • Run the lvmdump command, which provides an information dump for diagnostic purposes. For information, see the lvmdump(8) man page.
  • Execute the lvs -v, pvs -a or dmsetup info -c command for additional system information.
  • Examine the last backup of the metadata in the /etc/lvm/backup file and archived versions in the /etc/lvm/archive file.
  • Check the current configuration information by running the lvm dumpconfig command.
  • Check the .cache file in the /etc/lvm directory for a record of which devices have physical volumes on them.

7.2. Displaying Information on Failed Devices
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You can use the -P argument of the lvs or vgs command to display information about a failed volume that would otherwise not appear in the output. This argument permits some operations even though the metatdata is not completely consistent internally. For example, if one of the devices that made up the volume group vg failed, the vgs command might show the following output. 
# vgs -o +devices
  Volume group "vg" not found
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If you specify the -P argument of the vgs command, the volume group is still unusable but you can see more information about the failed device. 
 vgs -P -o +devices
  Partial mode. Incomplete volume groups will be activated read-only.
  VG   #PV #LV #SN Attr   VSize VFree Devices
  vg     9   2   0 rz-pn- 2.11T 2.07T unknown device(0)
  vg     9   2   0 rz-pn- 2.11T 2.07T unknown device(5120),/dev/sda1(0)
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In this example, the failed device caused both a linear and a striped logical volume in the volume group to fail. The lvs command without the -P argument shows the following output. 
# lvs -a -o +devices
  Volume group "vg" not found
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Using the -P argument shows the logical volumes that have failed. 
# lvs -P -a -o +devices
  Partial mode. Incomplete volume groups will be activated read-only.
  LV     VG   Attr   LSize  Origin Snap%  Move Log Copy%  Devices
  linear vg   -wi-a- 20.00G                               unknown device(0)
  stripe vg   -wi-a- 20.00G                               unknown device(5120),/dev/sda1(0)
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The following examples show the output of the pvs and lvs commands with the -P argument specified when a leg of a mirrored logical volume has failed. 
#  vgs -a -o +devices -P
  Partial mode. Incomplete volume groups will be activated read-only.
  VG    #PV #LV #SN Attr   VSize VFree Devices
  corey   4   4   0 rz-pnc 1.58T 1.34T my_mirror_mimage_0(0),my_mirror_mimage_1(0)
  corey   4   4   0 rz-pnc 1.58T 1.34T /dev/sdd1(0)
  corey   4   4   0 rz-pnc 1.58T 1.34T unknown device(0)
  corey   4   4   0 rz-pnc 1.58T 1.34T /dev/sdb1(0)
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# lvs -a -o +devices -P
  Partial mode. Incomplete volume groups will be activated read-only.
  LV                   VG    Attr   LSize   Origin Snap%  Move Log            Copy%  Devices
  my_mirror            corey mwi-a- 120.00G                    my_mirror_mlog   1.95 my_mirror_mimage_0(0),my_mirror_mimage_1(0)
  [my_mirror_mimage_0] corey iwi-ao 120.00G                                          unknown device(0)
  [my_mirror_mimage_1] corey iwi-ao 120.00G                                          /dev/sdb1(0)
  [my_mirror_mlog]     corey lwi-ao   4.00M                                          /dev/sdd1(0)
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7.3. Recovering from LVM Mirror Failure
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This section provides an example of recovering from a situation where one leg of an LVM mirrored volume fails because the underlying device for a physical volume goes down. When a mirror leg fails, LVM converts the mirrored volume into a linear volume, which continues to operate as before but without the mirrored redundancy. At that point, you can add a new disk device to the system to use as a replacement physical device and rebuild the mirror.
The following command creates the physical volumes which will be used for the mirror. 
# pvcreate /dev/sd[abcdefgh][12]
  Physical volume "/dev/sda1" successfully created
  Physical volume "/dev/sda2" successfully created
  Physical volume "/dev/sdb1" successfully created
  Physical volume "/dev/sdb2" successfully created
  Physical volume "/dev/sdc1" successfully created
  Physical volume "/dev/sdc2" successfully created
  Physical volume "/dev/sdd1" successfully created
  Physical volume "/dev/sdd2" successfully created
  Physical volume "/dev/sde1" successfully created
  Physical volume "/dev/sde2" successfully created
  Physical volume "/dev/sdf1" successfully created
  Physical volume "/dev/sdf2" successfully created
  Physical volume "/dev/sdg1" successfully created
  Physical volume "/dev/sdg2" successfully created
  Physical volume "/dev/sdh1" successfully created
  Physical volume "/dev/sdh2" successfully created
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The following commands creates the volume group vg and the mirrored volume groupfs. 
# vgcreate vg /dev/sd[abcdefgh][12]
  Volume group "vg" successfully created
# lvcreate -L 750M -n groupfs -m 1 vg /dev/sda1 /dev/sdb1 /dev/sdc1
  Rounding up size to full physical extent 752.00 MB
  Logical volume "groupfs" created
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You can use the lvs command to verify the layout of the mirrored volume and the underlying devices for the mirror leg and the mirror log. Note that in the first example the mirror is not yet completely synced; you should wait until the Copy% field displays 100.00 before continuing. 
# lvs -a -o +devices
  LV                 VG   Attr   LSize   Origin Snap%  Move Log          Copy% Devices
  groupfs            vg   mwi-a- 752.00M                    groupfs_mlog 21.28 groupfs_mimage_0(0),groupfs_mimage_1(0)
  [groupfs_mimage_0] vg   iwi-ao 752.00M                                       /dev/sda1(0)
  [groupfs_mimage_1] vg   iwi-ao 752.00M                                       /dev/sdb1(0)
  [groupfs_mlog]     vg   lwi-ao   4.00M                                       /dev/sdc1(0)

# lvs -a -o +devices
  LV                 VG   Attr   LSize   Origin Snap%  Move Log          Copy%  Devices
  groupfs            vg   mwi-a- 752.00M                    groupfs_mlog 100.00 groupfs_mimage_0(0),groupfs_mimage_1(0)
  [groupfs_mimage_0] vg   iwi-ao 752.00M                                        /dev/sda1(0)
  [groupfs_mimage_1] vg   iwi-ao 752.00M                                        /dev/sdb1(0)
  [groupfs_mlog]     vg   lwi-ao   4.00M     i                                  /dev/sdc1(0)
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In this example, the primary leg of the mirror /dev/sda1 fails. Any write activity to the mirrored volume causes LVM to detect the failed mirror. When this occurs, LVM converts the mirror into a single linear volume. In this case, to trigger the conversion, we execute a dd command 
# dd if=/dev/zero of=/dev/vg/groupfs count=10
10+0 records in
10+0 records out
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You can use the lvs command to verify that the device is now a linear device. Because of the failed disk, I/O errors occur. 
# lvs -a -o +devices
  /dev/sda1: read failed after 0 of 2048 at 0: Input/output error
  /dev/sda2: read failed after 0 of 2048 at 0: Input/output error
  LV      VG   Attr   LSize   Origin Snap%  Move Log Copy%  Devices
  groupfs vg   -wi-a- 752.00M                               /dev/sdb1(0)
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At this point you should still be able to use the logical volume, but there will be no mirror redundancy.
To rebuild the mirrored volume, you replace the broken drive and recreate the physical volume. If you use the same disk rather than replacing it with a new one, you will see "inconsistent" warnings when you run the pvcreate command. 
# pvcreate /dev/sda[12]
  Physical volume "/dev/sda1" successfully created
  Physical volume "/dev/sda2" successfully created

# pvscan
  PV /dev/sdb1   VG vg   lvm2 [67.83 GB / 67.10 GB free]
  PV /dev/sdb2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdc1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdc2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdd1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdd2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sde1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sde2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdf1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdf2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdg1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdg2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdh1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdh2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sda1           lvm2 [603.94 GB]
  PV /dev/sda2           lvm2 [603.94 GB]
  Total: 16 [2.11 TB] / in use: 14 [949.65 GB] / in no VG: 2 [1.18 TB]
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Next you extend the original volume group with the new physical volume. 
# vgextend vg /dev/sda[12]
  Volume group "vg" successfully extended

# pvscan
  PV /dev/sdb1   VG vg   lvm2 [67.83 GB / 67.10 GB free]
  PV /dev/sdb2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdc1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdc2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdd1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdd2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sde1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sde2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdf1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdf2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdg1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdg2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdh1   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sdh2   VG vg   lvm2 [67.83 GB / 67.83 GB free]
  PV /dev/sda1   VG vg   lvm2 [603.93 GB / 603.93 GB free]
  PV /dev/sda2   VG vg   lvm2 [603.93 GB / 603.93 GB free]
  Total: 16 [2.11 TB] / in use: 16 [2.11 TB] / in no VG: 0 [0   ]
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Convert the linear volume back to its original mirrored state. 
# lvconvert -m 1 /dev/vg/groupfs /dev/sda1 /dev/sdb1 /dev/sdc1
  Logical volume mirror converted.
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You can use the lvs command to verify that the mirror is restored. 
# lvs -a -o +devices
  LV                 VG   Attr   LSize   Origin Snap%  Move Log          Copy% Devices
  groupfs            vg   mwi-a- 752.00M                    groupfs_mlog 68.62 groupfs_mimage_0(0),groupfs_mimage_1(0)
  [groupfs_mimage_0] vg   iwi-ao 752.00M                                       /dev/sdb1(0)
  [groupfs_mimage_1] vg   iwi-ao 752.00M                                       /dev/sda1(0)
  [groupfs_mlog]     vg   lwi-ao   4.00M                                       /dev/sdc1(0)
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7.4. Recovering Physical Volume Metadata
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If the volume group metadata area of a physical volume is accidentally overwritten or otherwise destroyed, you will get an error message indicating that the metadata area is incorrect, or that the system was unable to find a physical volume with a particular UUID. You may be able to recover the data the physical volume by writing a new metadata area on the physical volume specifying the same UUID as the lost metadata.

Warning

You should not attempt this procedure with a working LVM logical volume. You will lose your data if you specify the incorrect UUID.
The following example shows the sort of output you may see if the metadata area is missing or corrupted. 
# lvs -a -o +devices
  Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
  Couldn't find all physical volumes for volume group VG.
  Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
  Couldn't find all physical volumes for volume group VG.
  ...
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You may be able to find the UUID for the physical volume that was overwritten by looking in the /etc/lvm/archive directory. Look in the file VolumeGroupName_xxxx.vg for the last known valid archived LVM metadata for that volume group.
Alternately, you may find that deactivating the volume and setting the partial (-P) argument will enable you to find the UUID of the missing corrupted physical volume. 
# vgchange -an --partial
  Partial mode. Incomplete volume groups will be activated read-only.
  Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
  Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
  ...
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Use the --uuid and --restorefile arguments of the pvcreate command to restore the physical volume. The following example labels the /dev/sdh1 device as a physical volume with the UUID indicated above, FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk. This command restores the physical volume label with the metadata information contained in VG_00050.vg, the most recent good archived metatdata for volume group . The restorefile argument instructs the pvcreate command to make the new physical volume compatible with the old one on the volume group, ensuring that the new metadata will not be placed where the old physical volume contained data (which could happen, for example, if the original pvcreate command had used the command line arguments that control metadata placement, or it the physical volume was originally created using a different version of the software that used different defaults). The pvcreate command overwrites only the LVM metadata areas and does not affect the existing data areas. 
# pvcreate --uuid "FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk" --restorefile /etc/lvm/archive/VG_00050.vg /dev/sdh1
  Physical volume "/dev/sdh1" successfully created
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You can then use the vgcfgrestore command to restore the volume group's metadata. 
# vgcfgrestore VG
  Restored volume group VG
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You can now display the logical volumes. 
# lvs -a -o +devices
  LV     VG   Attr   LSize   Origin Snap%  Move Log Copy%  Devices
  stripe VG   -wi--- 300.00G                               /dev/sdh1 (0),/dev/sda1(0)
  stripe VG   -wi--- 300.00G                               /dev/sdh1 (34728),/dev/sdb1(0)
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The following commands activate the volumes and display the active volumes. 
# lvchange -ay /dev/VG/stripe
# lvs -a -o +devices
  LV     VG   Attr   LSize   Origin Snap%  Move Log Copy%  Devices
  stripe VG   -wi-a- 300.00G                               /dev/sdh1 (0),/dev/sda1(0)
  stripe VG   -wi-a- 300.00G                               /dev/sdh1 (34728),/dev/sdb1(0)
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If the on-disk LVM metadata takes as least as much space as what overrode it, this command can recover the physical volume. If what overrode the metadata went past the metadata area, the data on the volume may have been affected. You might be able to use the fsck command to recover that data.

7.5. Replacing a Missing Physical Volume
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If a physical volume fails or otherwise needs to be replaced, you can label a new physical volume to replace the one that has been lost in the existing volume group by following the same procedure as you would for recovering physical volume metadata, described in Section 7.4, “Recovering Physical Volume Metadata”. You can use the --partial and --verbose arguments of the vgdisplay command to display the UUIDs and sizes of any physical volumes that are no longer present. If you wish to substitute another physical volume of the same size, you can use the pvcreate command with the --restorefile and --uuid arguments to initialize a new device with the same UUID as the missing physical volume. You can then use the vgcfgrestore command to restore the volume group's metadata.
If you lose a physical volume, you can activate the remaining physical volumes in the volume group with the --partial argument of the vgchange command. You can remove all the logical volumes that used that physical volume from the volume group with the --removemissing argument of the vgreduce command.
It is recommended that you run the vgreduce command with the --test argument to verify what you will be destroying.
Like most LVM operations, the vgreduce command is reversible in a sense if you immediately use the vgcfgrestore command to restore the volume group metadata to its previous state. For example, if you used the --removemissing argument of the vgreduce command without the --test argument and find you have removed logical volumes you wanted to keep, you can still replace the physical volume and use another vgcfgrestore command to return the volume group to its previous state.
You may get the error message "Insufficient free extents" when creating a logical volume when you think you have enough extents based on the output of the vgdisplay or vgs commands. This is because these commands round figures to 2 decimal places to provide human-readable output. To specify exact size, use free physical extent count instead of some multiple of bytes to determine the size of the logical volume.
The vgdisplay command, by default, includes this line of output that indicates the free physical extents. 
# vgdisplay
  --- Volume group ---
  ...
  Free  PE / Size       8780 / 34.30 GB
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Alternately, you can use the vg_free_count and vg_extent_count arguments of the vgs command to display the free extents and the total number of extents. 
# vgs -o +vg_free_count,vg_extent_count
  VG     #PV #LV #SN Attr   VSize  VFree  Free #Ext
  testvg   2   0   0 wz--n- 34.30G 34.30G 8780 8780
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With 8780 free physical extents, you can run the following command, using the lower-case l argument to use extents instead of bytes: 
# lvcreate -l8780 -n testlv testvg
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This uses all the free extents in the volume group. 
# vgs -o +vg_free_count,vg_extent_count
  VG     #PV #LV #SN Attr   VSize  VFree Free #Ext
  testvg   2   1   0 wz--n- 34.30G    0     0 8780
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Alternately, you can extend the logical volume to use a percentage of the remaining free space in the volume group by using the -l argument of the lvcreate command. For information, see Section 5.4.1.1, “Creating Linear Volumes”.

Chapter 8. LVM Administration with the LVM GUI
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In addition to the Command Line Interface (CLI), LVM provides a Graphical User Interface (GUI) which you can use to configure LVM logical volumes. You can bring up this utility by typing system-config-lvm. The LVM chapter of the Red Hat Enterprise Linux Deployment Guide provides step-by-step instructions for configuring an LVM logical volume using this utility.
In addition, the LVM GUI is available as part of the Conga management interface. For information on using the LVM GUI with Conga, see the online help for Conga.

Appendix A. The Device Mapper
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The Device Mapper is a kernel driver that provides a framework for volume management. It provides a generic way of creating mapped devices, which may be used as logical volumes. It does not specifically know about volume groups or metadata formats.
The Device Mapper provides the foundation for a number of higher-level technologies. In addition to LVM, Device-Mapper multipath and the dmraid command use the Device Mapper. The application interface to the Device Mapper is the ioctl system call. The user interface is the dmsetup command.
LVM logical volumes are activated using the Device Mapper. Each logical volume is translated into a mapped device. Each segment translates into a line in the mapping table that describes the device. The Device Mapper supports a variety of mapping targets, including linear mapping, striped mapping, and error mapping. So, for example, two disks may be concatenated into one logical volume with a pair of linear mappings, one for each disk. When LVM2 creates a volume, it creates an underlying device-mapper device that can be queried with the dmsetup command. For information about the format of devices in a mapping table, see Section A.1, “Device Table Mappings”. For information about using the dmsetup command to query a device, see Section A.2, “The dmsetup Command”.

A.1. Device Table Mappings
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A mapped device is defined by a table that specifies how to map each range of logical sectors of the device using a supported Device Table mapping. The table for a mapped device is constructed from a list of lines of the form: 
start length mapping [mapping_parameters...]
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In the first line of a Device Mapper table, the start parameter must equal 0. The start + length parameters on one line must equal the start on the next line. Which mapping parameters are specified in a line of the mapping table depends on which mapping type is specified on the line.
Sizes in the Device Mapper are always specified in sectors (512 bytes).
When a device is specified as a mapping parameter in the Device Mapper, it can be referenced by the device name in the filesystem (for example, /dev/hda) or by the major and minor numbers in the format major:minor. The major:minor format is preferred because it avoids pathname lookups.
The following shows a sample mapping table for a device. In this table there are four linear targets: 
0 35258368 linear 8:48 65920
35258368 35258368 linear 8:32 65920
70516736 17694720 linear 8:16 17694976
88211456 17694720 linear 8:16 256
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The first 2 parameters of each line are the segment starting block and the length of the segment. The next keyword is the mapping target, which in all of the cases in this example is linear. The rest of the line consists of the parameters for a linear target.
The following subsections describe the format of the following mappings:
  • linear
  • striped
  • mirror
  • snapshot and snapshot-origin
  • error
  • zero
  • multipath
  • crypt

A.1.1. The linear Mapping Target
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A linear mapping target maps a continuous range of blocks onto another block device. The format of a linear target is as follows: 
start length linear device offset
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start
starting block in virtual device
length
length of this segment
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in the format major:minor
offset
starting offset of the mapping on the device
The following example shows a linear target with a starting block in the virtual device of 0, a segment length of 1638400, a major:minor number pair of 8:2, and a starting offset for the device of 41146992. 
0 16384000 linear 8:2 41156992
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The following example shows a linear target with the device parameter specified as the device /dev/hda. 
0 20971520 linear /dev/hda 384
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A.1.2. The striped Mapping Target
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The striped mapping target supports striping across physical devices. It takes as arguments the number of stripes and the striping chunk size followed by a list of pairs of device name and sector. The format of a striped target is as follows: 
start length striped #stripes chunk_size device1 offset1 ... deviceN offsetN
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There is one set of device and offset parameters for each stripe.
start
starting block in virtual device
length
length of this segment
#stripes
number of stripes for the virtual device
chunk_size
number of sectors written to each stripe before switching to the next; must be power of 2 at least as big as the kernel page size
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in the format major:minor.
offset
starting offset of the mapping on the device
The following example shows a striped target with three stripes and a chunk size of 128: 
0 73728 striped 3 128 8:9 384 8:8 384 8:7 9789824
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0
starting block in virtual device
73728
length of this segment
striped 3 128
stripe across three devices with chunk size of 128 blocks
8:9
major:minor numbers of first device
384
starting offset of the mapping on the first device
8:8
major:minor numbers of second device
384
starting offset of the mapping on the second device
8:7
major:minor numbers of third device
9789824
starting offset of the mapping on the third device
The following example shows a striped target for 2 stripes with 256 KiB chunks, with the device parameters specified by the device names in the file system rather than by the major and minor numbers. 
0 65536 striped 2 512 /dev/hda 0 /dev/hdb 0
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A.1.3. The mirror Mapping Target
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The mirror mapping target supports the mapping of a mirrored logical device. The format of a mirrored target is as follows: 
start length mirror log_type #logargs logarg1 ... logargN #devs device1 offset1 ... deviceN offsetN
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start
starting block in virtual device
length
length of this segment
log_type
The possible log types and their arguments are as follows:
core
The mirror is local and the mirror log is kept in core memory. This log type takes 1 - 3 arguments:
regionsize [[no]sync] [block_on_error]
disk
The mirror is local and the mirror log is kept on disk. This log type takes 2 - 4 arguments:
logdevice regionsize [[no]sync] [block_on_error]
clustered_core
The mirror is clustered and the mirror log is kept in core memory. This log type takes 2 - 4 arguments:
regionsize UUID [[no]sync] [block_on_error]
clustered_disk
The mirror is clustered and the mirror log is kept on disk. This log type takes 3 - 5 arguments:
logdevice regionsize UUID [[no]sync] [block_on_error]
LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or mirrors. The regionsize argument specifies the size of these regions.
In a clustered environment, the UUID argument is a unique identifier associated with the mirror log device so that the log state can be maintained throughout the cluster.
The optional [no]sync argument can be used to specify the mirror as "in-sync" or "out-of-sync". The block_on_error argument is used to tell the mirror to respond to errors rather than ignoring them.
#log_args
number of log arguments that will be specified in the mapping
logargs
the log arguments for the mirror; the number of log arguments provided is specified by the #log-args parameter and the valid log arguments are determined by the log_type parameter.
#devs
the number of legs in the mirror; a device and an offset is specified for each leg.
device
block device for each mirror leg, referenced by the device name in the filesystem or by the major and minor numbers in the format major:minor. A block device and offset is specified for each mirror leg, as indicated by the #devs parameter.
offset
starting offset of the mapping on the device. A block device and offset is specified for each mirror leg, as indicated by the #devs parameter.
The following example shows a mirror mapping target for a clustered mirror with a mirror log kept on disk. 
0 52428800 mirror clustered_disk 4 253:2 1024 UUID block_on_error 3 253:3 0 253:4 0 253:5 0
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0
starting block in virtual device
52428800
length of this segment
mirror clustered_disk
mirror target with a log type specifying that mirror is clustered and the mirror log is maintained on disk
4
4 mirror log arguments will follow
253:2
major:minor numbers of log device
1024
region size the mirror log uses to keep track of what is in sync
UUID
UUID of mirror log device to maintain log information throughout a cluster
block_on_error
mirror should respond to errors
3
number of legs in mirror
253:3 0 253:4 0 253:5 0
major:minor numbers and offset for devices constituting each leg of mirror
When you create the first LVM snapshot of a volume, four Device Mapper devices are used:
  1. A device with a linear mapping containing the original mapping table of the source volume.
  2. A device with a linear mapping used as the copy-on-write (COW) device for the source volume; for each write, the original data is saved in the COW device of each snapshot to keep its visible content unchanged (until the COW device fills up).
  3. A device with a snapshot mapping combining #1 and #2, which is the visible snapshot volume
  4. The "original" volume (which uses the device number used by the original source volume), whose table is replaced by a "snapshot-origin" mapping from device #1.
A fixed naming scheme is used to create these devices, For example, you might use the following commands to create an LVM volume named base and a snapshot volume named snap based on that volume. 
# lvcreate -L 1G -n base volumeGroup
# lvcreate -L 100M --snapshot -n snap volumeGroup/base
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This yields four devices, which you can view with the following commands: 
# dmsetup table|grep volumeGroup
volumeGroup-base-real: 0 2097152 linear 8:19 384
volumeGroup-snap-cow: 0 204800 linear 8:19 2097536
volumeGroup-snap: 0 2097152 snapshot 254:11 254:12 P 16
volumeGroup-base: 0 2097152 snapshot-origin 254:11

# ls -lL /dev/mapper/volumeGroup-*
brw-------  1 root root 254, 11 29 ago 18:15 /dev/mapper/volumeGroup-base-real
brw-------  1 root root 254, 12 29 ago 18:15 /dev/mapper/volumeGroup-snap-cow
brw-------  1 root root 254, 13 29 ago 18:15 /dev/mapper/volumeGroup-snap
brw-------  1 root root 254, 10 29 ago 18:14 /dev/mapper/volumeGroup-base
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The format for the snapshot-origin target is as follows: 
start length snapshot-origin origin
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start
starting block in virtual device
length
length of this segment
origin
base volume of snapshot
The snapshot-origin will normally have one or more snapshots based on it. Reads will be mapped directly to the backing device. For each write, the original data will be saved in the COW device of each snapshot to keep its visible content unchanged until the COW device fills up.
The format for the snapshot target is as follows: 
start length snapshot origin COW-device P|N chunksize
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start
starting block in virtual device
length
length of this segment
origin
base volume of snapshot
COW-device
Device on which changed chunks of data are stored
P|N
P (Persistent) or N (Not persistent); indicates whether snapshot will survive after reboot. For transient snapshots (N) less metadata must be saved on disk; they can be kept in memory by the kernel.
chunksize
Size in sectors of changed chunks of data that will be stored on the COW device
The following example shows a snapshot-origin target with an origin device of 254:11. 
0 2097152 snapshot-origin 254:11
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The following example shows a snapshot target with an origin device of 254:11 and a COW device of 254:12. This snapshot device is persistent across reboots and the chunk size for the data stored on the COW device is 16 sectors. 
0 2097152 snapshot 254:11 254:12 P 16
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A.1.5. The error Mapping Target
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With an error mapping target, any I/O operation to the mapped sector fails.
An error mapping target can be used for testing. To test how a device behaves in failure, you can create a device mapping with a bad sector in the middle of a device, or you can swap out the leg of a mirror and replace the leg with an error target.
An error target can be used in place of a failing device, as a way of avoiding timeouts and retries on the actual device. It can serve as an intermediate target while you rearrange LVM metadata during failures.
The error mapping target takes no additional parameters besides the start and length parameters.
The following example shows an error target. 
0 65536 error
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A.1.6. The zero Mapping Target
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The zero mapping target is a block device equivalent of /dev/zero. A read operation to this mapping returns blocks of zeros. Data written to this mapping is discarded, but the write succeeds. The zero mapping target takes no additional parameters besides the start and length parameters.
The following example shows a zero target for a 16Tb Device. 
0 65536 zero
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A.1.7. The multipath Mapping Target
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The multipath mapping target supports the mapping of a multipathed device. The format for the multipath target is as follows: 
start length  multipath  #features [feature1 ... featureN] #handlerargs [handlerarg1 ... handlerargN] #pathgroups pathgroup pathgroupargs1 ... pathgroupargsN
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There is one set of pathgroupargs parameters for each path group.
start
starting block in virtual device
length
length of this segment
#features
The number of multipath features, followed by those features. If this parameter is zero, then there is no feature parameter and the next device mapping parameter is #handlerargs. Currently there is one supported feature that can be set with the features attribute in the multipath.conf file, queue_if_no_path. This indicates that this multipathed device is currently set to queue I/O operations if there is no path available.
In the following example, the no_path_retry attribute in the multipath.conf file has been set to queue I/O operations only until all paths have been marked as failed after a set number of attempts have been made to use the paths. In this case, the mapping appears as follows until all the path checkers have failed the specified number of checks. 
0 71014400 multipath 1 queue_if_no_path 0 2 1 round-robin 0 2 1 66:128 \
1000 65:64 1000 round-robin 0 2 1 8:0 1000 67:192 1000
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After all the path checkers have failed the specified number of checks, the mapping would appear as follows. 
0 71014400 multipath 0 0 2 1 round-robin 0 2 1 66:128 1000 65:64 1000 \
round-robin 0 2 1 8:0 1000 67:192 1000
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#handlerargs
The number of hardware handler arguments, followed by those arguments. A hardware handler specifies a module that will be used to perform hardware-specific actions when switching path groups or handling I/O errors. If this is set to 0, then the next parameter is #pathgroups.
#pathgroups
The number of path groups. A path group is the set of paths over which a multipathed device will load balance. There is one set of pathgroupargs parameters for each path group.
pathgroup
The next path group to try.
pathgroupsargs
Each path group consists of the following arguments: 
pathselector #selectorargs #paths #pathargs device1 ioreqs1 ... deviceN ioreqsN
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There is one set of path arguments for each path in the path group.
pathselector
Specifies the algorithm in use to determine what path in this path group to use for the next I/O operation.
#selectorargs
The number of path selector arguments which follow this argument in the multipath mapping. Currently, the value of this argument is always 0.
#paths
The number of paths in this path group.
#pathargs
The number of path arguments specified for each path in this group. Currently this number is always 1, the ioreqs argument.
device
The block device number of the path, referenced by the major and minor numbers in the format major:minor
ioreqs
The number of I/O requests to route to this path before switching to the next path in the current group.
Figure A.1, “Multipath Mapping Target” shows the format of a multipath target with two path groups.
Multipath Mapping Target
View larger image
Multipath Mapping Target

Figure A.1. Multipath Mapping Target

The following example shows a pure failover target definition for the same multipath device. In this target there are four path groups, with only one open path per path group so that the multipathed device will use only one path at a time. 
0 71014400 multipath 0 0 4 1 round-robin 0 1 1 66:112 1000 \
round-robin 0 1 1 67:176 1000 round-robin 0 1 1 68:240 1000 \
round-robin 0 1 1 65:48 1000
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The following example shows a full spread (multibus) target definition for the same multipathed device. In this target there is only one path group, which includes all of the paths. In this setup, multipath spreads the load evenly out to all of the paths. 
0 71014400 multipath 0 0 1 1 round-robin 0 4 1 66:112 1000 \
 67:176 1000 68:240 1000 65:48 1000
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For further information about multipathing, see the Using Device Mapper Multipath document.

A.1.8. The crypt Mapping Target
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The crypt target encrypts the data passing through the specified device. It uses the kernel Crypto API.
The format for the crypt target is as follows: 
start length crypt cipher key IV-offset device offset
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start
starting block in virtual device
length
length of this segment
cipher
Cipher consists of cipher[-chainmode]-ivmode[:iv options].
cipher
Ciphers available are listed in /proc/crypto (for example, aes).
chainmode
Always use cbc. Do not use ebc; it does not use an initial vector (IV).
ivmode[:iv options]
IV is an initial vector used to vary the encryption. The IV mode is plain or essiv:hash. An ivmode of -plain uses the sector number (plus IV offset) as the IV. An ivmode of -essiv is an enhancement avoiding a watermark weakness.
key
Encryption key, supplied in hex
IV-offset
Initial Vector (IV) offset
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in the format major:minor
offset
starting offset of the mapping on the device
The following is an example of a crypt target. 
0 2097152 crypt aes-plain 0123456789abcdef0123456789abcdef 0 /dev/hda 0
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A.2. The dmsetup Command
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The dmsetup command is a command line wrapper for communication with the Device Mapper. For general system information about LVM devices, you may find the info, ls, status, and deps options of the dmsetup command to be useful, as described in the following subsections.
For information about additional options and capabilities of the dmsetup command, see the dmsetup(8) man page.

A.2.1. The dmsetup info Command
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The dmsetup info device command provides summary information about Device Mapper devices. If you do not specify a device name, the output is information about all of the currently configured Device Mapper devices. If you specify a device, then this command yields information for that device only.
The dmsetup info command provides information in the following categories:
Name
The name of the device. An LVM device is expressed as the volume group name and the logical volume name separated by a hyphen. A hyphen in the original name is translated to two hyphens.
State
Possible device states are SUSPENDED, ACTIVE, and READ-ONLY. The dmsetup suspend command sets a device state to SUSPENDED. When a device is suspended, all I/O operations to that device stop. The dmsetup resume command restores a device state to ACTIVE.
Read Ahead
The number of data blocks that the system reads ahead for any open file on which read operations are ongoing. By default, the kernel chooses a suitable value automatically. You can change this value with the --readahead option of the dmsetup command.
Tables present
Possible states for this category are LIVE and INACTIVE. An INACTIVE state indicates that a table has been loaded which will be swapped in when a dmsetup resume command restores a device state to ACTIVE, at which point the table's state becomes LIVE. For information, see the dmsetup man page.
Open count
The open reference count indicates how many times the device is opened. A mount command opens a device.
Event number
The current number of events received. Issuing a dmsetup wait n command allows the user to wait for the n'th event, blocking the call until it is received.
Major, minor
Major and minor device number
Number of targets
The number of fragments that make up a device. For example, a linear device spanning 3 disks would have 3 targets. A linear device composed of the beginning and end of a disk, but not the middle would have 2 targets.
UUID
UUID of the device.
The following example shows partial output for the dmsetup info command. 
[root@ask-07 ~]# dmsetup info
Name:              testgfsvg-testgfslv1
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        0
Event number:      0
Major, minor:      253, 2
Number of targets: 2
UUID: LVM-K528WUGQgPadNXYcFrrf9LnPlUMswgkCkpgPIgYzSvigM7SfeWCypddNSWtNzc2N
...
Name:              VolGroup00-LogVol00
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        1
Event number:      0
Major, minor:      253, 0
Number of targets: 1
UUID: LVM-tOcS1kqFV9drb0X1Vr8sxeYP0tqcrpdegyqj5lZxe45JMGlmvtqLmbLpBcenh2L3
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A.2.2. The dmsetup ls Command
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You can list the device names of mapped devices with the dmsetup ls command. You can list devices that have at least one target of a specified type with the dmsetup ls --target target_type command. For other options of the dmsetup ls, see the dmsetup man page.
The following example shows the command to list the device names of currently configured mapped devices. 
# dmsetup ls
testgfsvg-testgfslv3    (253, 4)
testgfsvg-testgfslv2    (253, 3)
testgfsvg-testgfslv1    (253, 2)
VolGroup00-LogVol01     (253, 1)
VolGroup00-LogVol00     (253, 0)
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The following example shows the command to list the devices names of currently configured mirror mappings. 
# dmsetup ls --target mirror
lock_stress-grant--02.1722      (253, 34)
lock_stress-grant--01.1720      (253, 18)
lock_stress-grant--03.1718      (253, 52)
lock_stress-grant--02.1716      (253, 40)
lock_stress-grant--03.1713      (253, 47)
lock_stress-grant--02.1709      (253, 23)
lock_stress-grant--01.1707      (253, 8)
lock_stress-grant--01.1724      (253, 14)
lock_stress-grant--03.1711      (253, 27)
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A.2.3. The dmsetup status Command
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The dmsetup status device command provides status information for each target in a specified device. If you do not specify a device name, the output is information about all of the currently configured Device Mapper devices. You can list the status only of devices that have at least one target of a specified type with the dmsetup status --target target_type command.
The following example shows the command to list the status of the targets in all currently configured mapped devices. 
# dmsetup status
testgfsvg-testgfslv3: 0 312352768 linear 
testgfsvg-testgfslv2: 0 312352768 linear 
testgfsvg-testgfslv1: 0 312352768 linear 
testgfsvg-testgfslv1: 312352768 50331648 linear 
VolGroup00-LogVol01: 0 4063232 linear 
VolGroup00-LogVol00: 0 151912448 linear
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A.2.4. The dmsetup deps Command
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The dmsetup deps device command provides a list of (major, minor) pairs for devices referenced by the mapping table for the specified device. If you do not specify a device name, the output is information about all of the currently configured Device Mapper devices.
The following example shows the command to list the dependencies of all currently configured mapped devices. 
# dmsetup deps
testgfsvg-testgfslv3: 1 dependencies    : (8, 16)
testgfsvg-testgfslv2: 1 dependencies    : (8, 16)
testgfsvg-testgfslv1: 1 dependencies    : (8, 16)
VolGroup00-LogVol01: 1 dependencies     : (8, 2)
VolGroup00-LogVol00: 1 dependencies     : (8, 2)
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The following example shows the command to list the dependencies only of the device lock_stress-grant--02.1722: 
# dmsetup deps lock_stress-grant--02.1722
3 dependencies  : (253, 33) (253, 32) (253, 31)
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Appendix B. The LVM Configuration Files
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LVM supports multiple configuration files. At system startup, the lvm.conf configuration file is loaded from the directory specified by the environment variable LVM_SYSTEM_DIR, which is set to /etc/lvm by default.
The lvm.conf file can specify additional configuration files to load. Settings in later files override settings from earlier ones. To display the settings in use after loading all the configuration files, execute the lvm dumpconfig command.
For information on loading additional configuration files, see Section C.2, “Host Tags”.

B.1. The LVM Configuration Files
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The following files are used for LVM configuration:
/etc/lvm/lvm.conf
Central configuration file read by the tools.
etc/lvm/lvm_hosttag.conf
For each host tag, an extra configuration file is read if it exists: lvm_hosttag.conf. If that file defines new tags, then further configuration files will be appended to the list of files to read in. For information on host tags, see Section C.2, “Host Tags”.
In addition to the LVM configuration files, a system running LVM includes the following files that affect LVM system setup:
/etc/lvm/.cache
Device name filter cache file (configurable).
/etc/lvm/backup/
Directory for automatic volume group metadata backups (configurable).
/etc/lvm/archive/
Directory for automatic volume group metadata archives (configurable with regard to directory path and archive history depth).
/var/lock/lvm/
In single-host configuration, lock files to prevent parallel tool runs from corrupting the metadata; in a cluster, cluster-wide DLM is used.

B.2. Sample lvm.conf File
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The following is a sample lvm.conf configuration file. This configuration file is the default file for the Red Hat Enterprise Linux 5.9 release. If your system is running a different release of Red Hat Enterprise Linux, some of the default settings may differ. 
# This is an example configuration file for the LVM2 system.
# It contains the default settings that would be used if there was no
# /etc/lvm/lvm.conf file.
#
# Refer to 'man lvm.conf' for further information including the file layout.
#
# To put this file in a different directory and override /etc/lvm set
# the environment variable LVM_SYSTEM_DIR before running the tools.
#
# N.B. Take care that each setting only appears once if uncommenting
# example settings in this file.


# This section allows you to configure which block devices should
# be used by the LVM system.
devices {

    # Where do you want your volume groups to appear ?
    dir = "/dev"

    # An array of directories that contain the device nodes you wish
    # to use with LVM2.
    scan = [ "/dev" ]

    # If set, the cache of block device nodes with all associated symlinks
    # will be constructed out of the existing udev database content.
    # This avoids using and opening any inapplicable non-block devices or
    # subdirectories found in the device directory. This setting is applied
    # to udev-managed device directory only, other directories will be scanned
    # fully. LVM2 needs to be compiled with udev support for this setting to
    # take effect. N.B. Any device node or symlink not managed by udev in
    # udev directory will be ignored with this setting on.
    obtain_device_list_from_udev = 1

    # If several entries in the scanned directories correspond to the
    # same block device and the tools need to display a name for device,
    # all the pathnames are matched against each item in the following
    # list of regular expressions in turn and the first match is used.
    # preferred_names = [ ]

    # Try to avoid using undescriptive /dev/dm-N names, if present.
    preferred_names = [ "^/dev/mpath/", "^/dev/mapper/mpath", "^/dev/[hs]d" ]

    # A filter that tells LVM2 to only use a restricted set of devices.
    # The filter consists of an array of regular expressions.  These
    # expressions can be delimited by a character of your choice, and
    # prefixed with either an 'a' (for accept) or 'r' (for reject).
    # The first expression found to match a device name determines if
    # the device will be accepted or rejected (ignored).  Devices that
    # don't match any patterns are accepted.

    # Be careful if there there are symbolic links or multiple filesystem 
    # entries for the same device as each name is checked separately against
    # the list of patterns.  The effect is that if the first pattern in the 
    # list to match a name is an 'a' pattern for any of the names, the device
    # is accepted; otherwise if the first pattern in the list to match a name
    # is an 'r' pattern for any of the names it is rejected; otherwise it is
    # accepted.

    # Don't have more than one filter line active at once: only one gets used.

    # Run vgscan after you change this parameter to ensure that
    # the cache file gets regenerated (see below).
    # If it doesn't do what you expect, check the output of 'vgscan -vvvv'.


    # By default we accept every block device:
    filter = [ "a/.*/" ]

    # Exclude the cdrom drive
    # filter = [ "r|/dev/cdrom|" ]

    # When testing I like to work with just loopback devices:
    # filter = [ "a/loop/", "r/.*/" ]

    # Or maybe all loops and ide drives except hdc:
    # filter =[ "a|loop|", "r|/dev/hdc|", "a|/dev/ide|", "r|.*|" ]

    # Use anchors if you want to be really specific
    # filter = [ "a|^/dev/hda8$|", "r/.*/" ]

    # The results of the filtering are cached on disk to avoid
    # rescanning dud devices (which can take a very long time).
    # By default this cache is stored in the /etc/lvm/cache directory
    # in a file called '.cache'.
    # It is safe to delete the contents: the tools regenerate it.
    # (The old setting 'cache' is still respected if neither of
    # these new ones is present.)
    cache_dir = "/etc/lvm/cache"
    cache_file_prefix = ""

    # You can turn off writing this cache file by setting this to 0.
    write_cache_state = 1

    # Advanced settings.

    # List of pairs of additional acceptable block device types found 
    # in /proc/devices with maximum (non-zero) number of partitions.
    # types = [ "fd", 16 ]

    # If sysfs is mounted (2.6 kernels) restrict device scanning to 
    # the block devices it believes are valid.
    # 1 enables; 0 disables.
    sysfs_scan = 1

    # By default, LVM2 will ignore devices used as component paths
    # of device-mapper multipath devices.
    # 1 enables; 0 disables.
    multipath_component_detection = 1

    # By default, LVM2 will ignore devices used as components of
    # software RAID (md) devices by looking for md superblocks.
    # 1 enables; 0 disables.
    md_component_detection = 1

    # By default, if a PV is placed directly upon an md device, LVM2
    # will align its data blocks with the md device's stripe-width.
    # 1 enables; 0 disables.
    md_chunk_alignment = 1

    # Default alignment of the start of a data area in MB.  If set to 0,
    # a value of 64KB will be used.  Set to 1 for 1MiB, 2 for 2MiB, etc.
    # default_data_alignment = 1

    # By default, the start of a PV's data area will be a multiple of
    # the 'minimum_io_size' or 'optimal_io_size' exposed in sysfs.
    # - minimum_io_size - the smallest request the device can perform
    #   w/o incurring a read-modify-write penalty (e.g. MD's chunk size)
    # - optimal_io_size - the device's preferred unit of receiving I/O
    #   (e.g. MD's stripe width)
    # minimum_io_size is used if optimal_io_size is undefined (0).
    # If md_chunk_alignment is enabled, that detects the optimal_io_size.
    # This setting takes precedence over md_chunk_alignment.
    # 1 enables; 0 disables.
    data_alignment_detection = 1

    # Alignment (in KB) of start of data area when creating a new PV.
    # md_chunk_alignment and data_alignment_detection are disabled if set.
    # Set to 0 for the default alignment (see: data_alignment_default)
    # or page size, if larger.
    data_alignment = 0

    # By default, the start of the PV's aligned data area will be shifted by
    # the 'alignment_offset' exposed in sysfs.  This offset is often 0 but
    # may be non-zero; e.g.: certain 4KB sector drives that compensate for
    # windows partitioning will have an alignment_offset of 3584 bytes
    # (sector 7 is the lowest aligned logical block, the 4KB sectors start
    # at LBA -1, and consequently sector 63 is aligned on a 4KB boundary).
    # But note that pvcreate --dataalignmentoffset will skip this detection.
    # 1 enables; 0 disables.
    data_alignment_offset_detection = 1

    # If, while scanning the system for PVs, LVM2 encounters a device-mapper
    # device that has its I/O suspended, it waits for it to become accessible.
    # Set this to 1 to skip such devices.  This should only be needed
    # in recovery situations.
    ignore_suspended_devices = 0

    # During each LVM operation errors received from each device are counted.
    # If the counter of a particular device exceeds the limit set here, no
    # further I/O is sent to that device for the remainder of the respective
    # operation. Setting the parameter to 0 disables the counters altogether.
    disable_after_error_count = 0

    # Allow use of pvcreate --uuid without requiring --restorefile.
    require_restorefile_with_uuid = 1

    # Minimum size (in KB) of block devices which can be used as PVs.
    # In a clustered environment all nodes must use the same value.
    # Any value smaller than 512KB is ignored.

    # Ignore devices smaller than 2MB such as floppy drives.
    pv_min_size = 2048

    # The original built-in setting was 512 up to and including version 2.02.84.
    # pv_min_size = 512

    # Issue discards to a logical volumes's underlying physical volume(s) when
    # the logical volume is no longer using the physical volumes' space (e.g.
    # lvremove, lvreduce, etc).  Discards inform the storage that a region is
    # no longer in use.  Storage that supports discards advertise the protocol
    # specific way discards should be issued by the kernel (TRIM, UNMAP, or
    # WRITE SAME with UNMAP bit set).  Not all storage will support or benefit
    # from discards but SSDs and thinly provisioned LUNs generally do.  If set
    # to 1, discards will only be issued if both the storage and kernel provide
    # support.
    # 1 enables; 0 disables.
    issue_discards = 0
}

# This section allows you to configure the way in which LVM selects
# free space for its Logical Volumes.
#allocation {
#    When searching for free space to extend an LV, the "cling"
#    allocation policy will choose space on the same PVs as the last
#    segment of the existing LV.  If there is insufficient space and a
#    list of tags is defined here, it will check whether any of them are
#    attached to the PVs concerned and then seek to match those PV tags
#    between existing extents and new extents.
#    Use the special tag "@*" as a wildcard to match any PV tag.
#    
#    Example: LVs are mirrored between two sites within a single VG.
#    PVs are tagged with either @site1 or @site2 to indicate where
#    they are situated.
#
#    cling_tag_list = [ "@site1", "@site2" ]
#    cling_tag_list = [ "@*" ]
#
#    Changes made in version 2.02.85 extended the reach of the 'cling'
#    policies to detect more situations where data can be grouped
#    onto the same disks.  Set this to 0 to revert to the previous
#    algorithm.
#
#    maximise_cling = 1
#
#    Set to 1 to guarantee that mirror logs will always be placed on 
#    different PVs from the mirror images.  This was the default
#    until version 2.02.85.
#
#    mirror_logs_require_separate_pvs = 0
#
#    Set to 1 to guarantee that thin pool metadata will always
#    be placed on different PVs from the pool data.
#
#    thin_pool_metadata_require_separate_pvs = 0
#}

# This section that allows you to configure the nature of the
# information that LVM2 reports.
log {

    # Controls the messages sent to stdout or stderr.
    # There are three levels of verbosity, 3 being the most verbose.
    verbose = 0

    # Should we send log messages through syslog?
    # 1 is yes; 0 is no.
    syslog = 1

    # Should we log error and debug messages to a file?
    # By default there is no log file.
    #file = "/var/log/lvm2.log"

    # Should we overwrite the log file each time the program is run?
    # By default we append.
    overwrite = 0

    # What level of log messages should we send to the log file and/or syslog?
    # There are 6 syslog-like log levels currently in use - 2 to 7 inclusive.
    # 7 is the most verbose (LOG_DEBUG).
    level = 0

    # Format of output messages
    # Whether or not (1 or 0) to indent messages according to their severity
    indent = 1

    # Whether or not (1 or 0) to display the command name on each line output
    command_names = 0

    # A prefix to use before the message text (but after the command name,
    # if selected).  Default is two spaces, so you can see/grep the severity
    # of each message.
    prefix = "  "

    # To make the messages look similar to the original LVM tools use:
    #   indent = 0
    #   command_names = 1
    #   prefix = " -- "

    # Set this if you want log messages during activation.
    # Don't use this in low memory situations (can deadlock).
    # activation = 0
}

# Configuration of metadata backups and archiving.  In LVM2 when we
# talk about a 'backup' we mean making a copy of the metadata for the
# *current* system.  The 'archive' contains old metadata configurations.
# Backups are stored in a human readeable text format.
backup {

    # Should we maintain a backup of the current metadata configuration ?
    # Use 1 for Yes; 0 for No.
    # Think very hard before turning this off!
    backup = 1

    # Where shall we keep it ?
    # Remember to back up this directory regularly!
    backup_dir = "/etc/lvm/backup"

    # Should we maintain an archive of old metadata configurations.
    # Use 1 for Yes; 0 for No.
    # On by default.  Think very hard before turning this off.
    archive = 1

    # Where should archived files go ?
    # Remember to back up this directory regularly!
    archive_dir = "/etc/lvm/archive"

    # What is the minimum number of archive files you wish to keep ?
    retain_min = 10

    # What is the minimum time you wish to keep an archive file for ?
    retain_days = 30
}

# Settings for the running LVM2 in shell (readline) mode.
shell {

    # Number of lines of history to store in ~/.lvm_history
    history_size = 100
}


# Miscellaneous global LVM2 settings
global {

    # The file creation mask for any files and directories created.
    # Interpreted as octal if the first digit is zero.
    umask = 077

    # Allow other users to read the files
    #umask = 022

    # Enabling test mode means that no changes to the on disk metadata
    # will be made.  Equivalent to having the -t option on every
    # command.  Defaults to off.
    test = 0

    # Default value for --units argument
    units = "h"

    # Since version 2.02.54, the tools distinguish between powers of
    # 1024 bytes (e.g. KiB, MiB, GiB) and powers of 1000 bytes (e.g.
    # KB, MB, GB).
    # If you have scripts that depend on the old behaviour, set this to 0
    # temporarily until you update them.
    si_unit_consistency = 1

    # Whether or not to communicate with the kernel device-mapper.
    # Set to 0 if you want to use the tools to manipulate LVM metadata 
    # without activating any logical volumes.
    # If the device-mapper kernel driver is not present in your kernel
    # setting this to 0 should suppress the error messages.
    activation = 1

    # If we can't communicate with device-mapper, should we try running 
    # the LVM1 tools?
    # This option only applies to 2.4 kernels and is provided to help you
    # switch between device-mapper kernels and LVM1 kernels.
    # The LVM1 tools need to be installed with .lvm1 suffices
    # e.g. vgscan.lvm1 and they will stop working after you start using
    # the new lvm2 on-disk metadata format.
    # The default value is set when the tools are built.
    # fallback_to_lvm1 = 0

    # The default metadata format that commands should use - "lvm1" or "lvm2".
    # The command line override is -M1 or -M2.
    # Defaults to "lvm2".
    # format = "lvm2"

    # Location of proc filesystem
    proc = "/proc"

    # Type of locking to use. Defaults to local file-based locking (1).
    # Turn locking off by setting to 0 (dangerous: risks metadata corruption
    # if LVM2 commands get run concurrently).
    # Type 2 uses the external shared library locking_library.
    # Type 3 uses built-in clustered locking.
    # Type 4 uses read-only locking which forbids any operations that might 
    # change metadata.
    locking_type = 1

    # Set to 0 to fail when a lock request cannot be satisfied immediately.
    wait_for_locks = 1

    # If using external locking (type 2) and initialisation fails,
    # with this set to 1 an attempt will be made to use the built-in
    # clustered locking.
    # If you are using a customised locking_library you should set this to 0.
    fallback_to_clustered_locking = 1

    # If an attempt to initialise type 2 or type 3 locking failed, perhaps
    # because cluster components such as clvmd are not running, with this set
    # to 1 an attempt will be made to use local file-based locking (type 1).
    # If this succeeds, only commands against local volume groups will proceed.
    # Volume Groups marked as clustered will be ignored.
    fallback_to_local_locking = 1

    # Local non-LV directory that holds file-based locks while commands are
    # in progress.  A directory like /tmp that may get wiped on reboot is OK.
    locking_dir = "/var/lock/lvm"

    # Whenever there are competing read-only and read-write access requests for
    # a volume group's metadata, instead of always granting the read-only
    # requests immediately, delay them to allow the read-write requests to be
    # serviced.  Without this setting, write access may be stalled by a high
    # volume of read-only requests.
    # NB. This option only affects locking_type = 1 viz. local file-based
    # locking.
    prioritise_write_locks = 1

    # Other entries can go here to allow you to load shared libraries
    # e.g. if support for LVM1 metadata was compiled as a shared library use
    #   format_libraries = "liblvm2format1.so" 
    # Full pathnames can be given.

    # Search this directory first for shared libraries.
    #   library_dir = "/lib"

    # The external locking library to load if locking_type is set to 2.
    #   locking_library = "liblvm2clusterlock.so"

    # Treat any internal errors as fatal errors, aborting the process that
    # encountered the internal error. Please only enable for debugging.
    abort_on_internal_errors = 0

    # Check whether CRC is matching when parsed VG is used multiple times.
    # This is useful to catch unexpected internal cached volume group
    # structure modification. Please only enable for debugging.
    detect_internal_vg_cache_corruption = 0

    # If set to 1, no operations that change on-disk metadata will be permitted.
    # Additionally, read-only commands that encounter metadata in need of repair
    # will still be allowed to proceed exactly as if the repair had been 
    # performed (except for the unchanged vg_seqno).
    # Inappropriate use could mess up your system, so seek advice first!
    metadata_read_only = 0

    # 'mirror_segtype_default' defines which segtype will be used when the
    # shorthand '-m' option is used for mirroring.  The possible options are:
    #
    # "mirror" - The original RAID1 implementation provided by LVM2/DM.  It is
    # 	         characterized by a flexible log solution (core, disk, mirrored)
    #		 and by the necessity to block I/O while reconfiguring in the
    #		 event of a failure.
    #
    #		 There is an inherent race in the dmeventd failure handling
    #		 logic with snapshots of devices using this type of RAID1 that
    #		 in the worst case could cause a deadlock.
    #		   Ref: https://bugzilla.redhat.com/show_bug.cgi?id=817130#c10
    #
    # "raid1"  - This implementation leverages MD's RAID1 personality through
    # 	       	 device-mapper.  It is characterized by a lack of log options.
    #		 (A log is always allocated for every device and they are placed
    #		 on the same device as the image - no separate devices are
    #		 required.)  This mirror implementation does not require I/O
    #		 to be blocked in the kernel in the event of a failure.
    #		 This mirror implementation is not cluster-aware and cannot be
    #		 used in a shared (active/active) fashion in a cluster.
    #
    # Specify the '--type <mirror|raid1>' option to override this default
    # setting.
    mirror_segtype_default = "mirror"

    # The default format for displaying LV names in lvdisplay was changed 
    # in version 2.02.89 to show the LV name and path separately.
    # Previously this was always shown as /dev/vgname/lvname even when that
    # was never a valid path in the /dev filesystem.
    # Set to 1 to reinstate the previous format.
    #
    # lvdisplay_shows_full_device_path = 0

    # Whether to use (trust) a running instance of lvmetad. If this is set to
    # 0, all commands fall back to the usual scanning mechanisms. When set to 1
    # *and* when lvmetad is running (it is not auto-started), the volume group
    # metadata and PV state flags are obtained from the lvmetad instance and no
    # scanning is done by the individual commands. In a setup with lvmetad,
    # lvmetad udev rules *must* be set up for LVM to work correctly. Without
    # proper udev rules, all changes in block device configuration will be
    # *ignored* until a manual 'vgscan' is performed.
    use_lvmetad = 0
}

activation {
    # Set to 1 to perform internal checks on the operations issued to
    # libdevmapper.  Useful for debugging problems with activation.
    # Some of the checks may be expensive, so it's best to use this
    # only when there seems to be a problem.
    checks = 0

    # Set to 0 to disable udev synchronisation (if compiled into the binaries).
    # Processes will not wait for notification from udev.
    # They will continue irrespective of any possible udev processing
    # in the background.  You should only use this if udev is not running
    # or has rules that ignore the devices LVM2 creates.
    # The command line argument --nodevsync takes precedence over this setting.
    # If set to 1 when udev is not running, and there are LVM2 processes
    # waiting for udev, run 'dmsetup udevcomplete_all' manually to wake them up.
    udev_sync = 1

    # Set to 0 to disable the udev rules installed by LVM2 (if built with
    # --enable-udev_rules). LVM2 will then manage the /dev nodes and symlinks
    # for active logical volumes directly itself.
    # N.B. Manual intervention may be required if this setting is changed
    # while any logical volumes are active.
    udev_rules = 1

    # Set to 1 for LVM2 to verify operations performed by udev. This turns on
    # additional checks (and if necessary, repairs) on entries in the device
    # directory after udev has completed processing its events. 
    # Useful for diagnosing problems with LVM2/udev interactions.
    verify_udev_operations = 0

    # If set to 1 and if deactivation of an LV fails, perhaps because
    # a process run from a quick udev rule temporarily opened the device,
    # retry the operation for a few seconds before failing.
    retry_deactivation = 1

    # How to fill in missing stripes if activating an incomplete volume.
    # Using "error" will make inaccessible parts of the device return
    # I/O errors on access.  You can instead use a device path, in which 
    # case, that device will be used to in place of missing stripes.
    # But note that using anything other than "error" with mirrored 
    # or snapshotted volumes is likely to result in data corruption.
    missing_stripe_filler = "error"

    # The linear target is an optimised version of the striped target
    # that only handles a single stripe.  Set this to 0 to disable this
    # optimisation and always use the striped target.
    use_linear_target = 1

    # How much stack (in KB) to reserve for use while devices suspended
    # Prior to version 2.02.89 this used to be set to 256KB
    reserved_stack = 64

    # How much memory (in KB) to reserve for use while devices suspended
    reserved_memory = 8192

    # Nice value used while devices suspended
    process_priority = -18

    # If volume_list is defined, each LV is only activated if there is a
    # match against the list.
    #   "vgname" and "vgname/lvname" are matched exactly.
    #   "@tag" matches any tag set in the LV or VG.
    #   "@*" matches if any tag defined on the host is also set in the LV or VG
    #
    # volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

    # If read_only_volume_list is defined, each LV that is to be activated 
    # is checked against the list, and if it matches, it as activated
    # in read-only mode.  (This overrides '--permission rw' stored in the
    # metadata.)
    #   "vgname" and "vgname/lvname" are matched exactly.
    #   "@tag" matches any tag set in the LV or VG.
    #   "@*" matches if any tag defined on the host is also set in the LV or VG
    #
    # read_only_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

    # Size (in KB) of each copy operation when mirroring
    mirror_region_size = 512

    # Setting to use when there is no readahead value stored in the metadata.
    #
    # "none" - Disable readahead.
    # "auto" - Use default value chosen by kernel.
    readahead = "auto"

    # 'raid_fault_policy' defines how a device failure in a RAID logical
    # volume is handled.  This includes logical volumes that have the following
    # segment types: raid1, raid4, raid5*, and raid6*.
    #
    # In the event of a failure, the following policies will determine what
    # actions are performed during the automated response to failures (when
    # dmeventd is monitoring the RAID logical volume) and when 'lvconvert' is
    # called manually with the options '--repair' and '--use-policies'.
    #
    # "warn"	- Use the system log to warn the user that a device in the RAID
    # 		  logical volume has failed.  It is left to the user to run
    #		  'lvconvert --repair' manually to remove or replace the failed
    #		  device.  As long as the number of failed devices does not
    #		  exceed the redundancy of the logical volume (1 device for
    #		  raid4/5, 2 for raid6, etc) the logical volume will remain
    #		  usable.
    #
    # "allocate" - Attempt to use any extra physical volumes in the volume
    # 		  group as spares and replace faulty devices.
    #
    raid_fault_policy = "warn"

    # 'mirror_image_fault_policy' and 'mirror_log_fault_policy' define
    # how a device failure affecting a mirror (of "mirror" segment type) is
    # handled.  A mirror is composed of mirror images (copies) and a log.
    # A disk log ensures that a mirror does not need to be re-synced
    # (all copies made the same) every time a machine reboots or crashes.
    #
    # In the event of a failure, the specified policy will be used to determine
    # what happens. This applies to automatic repairs (when the mirror is being
    # monitored by dmeventd) and to manual lvconvert --repair when
    # --use-policies is given.
    #
    # "remove" - Simply remove the faulty device and run without it.  If
    #            the log device fails, the mirror would convert to using
    #            an in-memory log.  This means the mirror will not
    #            remember its sync status across crashes/reboots and
    #            the entire mirror will be re-synced.  If a
    #            mirror image fails, the mirror will convert to a
    #            non-mirrored device if there is only one remaining good
    #            copy.
    #
    # "allocate" - Remove the faulty device and try to allocate space on
    #            a new device to be a replacement for the failed device.
    #            Using this policy for the log is fast and maintains the
    #            ability to remember sync state through crashes/reboots.
    #            Using this policy for a mirror device is slow, as it
    #            requires the mirror to resynchronize the devices, but it
    #            will preserve the mirror characteristic of the device.
    #            This policy acts like "remove" if no suitable device and
    #            space can be allocated for the replacement.
    #
    # "allocate_anywhere" - Not yet implemented. Useful to place the log device
    #            temporarily on same physical volume as one of the mirror
    #            images. This policy is not recommended for mirror devices
    #            since it would break the redundant nature of the mirror. This
    #            policy acts like "remove" if no suitable device and space can
    #            be allocated for the replacement.

    mirror_log_fault_policy = "allocate"
    mirror_image_fault_policy = "remove"

    # 'snapshot_autoextend_threshold' and 'snapshot_autoextend_percent' define
    # how to handle automatic snapshot extension. The former defines when the
    # snapshot should be extended: when its space usage exceeds this many
    # percent. The latter defines how much extra space should be allocated for
    # the snapshot, in percent of its current size.
    #
    # For example, if you set snapshot_autoextend_threshold to 70 and
    # snapshot_autoextend_percent to 20, whenever a snapshot exceeds 70% usage,
    # it will be extended by another 20%. For a 1G snapshot, using up 700M will
    # trigger a resize to 1.2G. When the usage exceeds 840M, the snapshot will
    # be extended to 1.44G, and so on.
    #
    # Setting snapshot_autoextend_threshold to 100 disables automatic
    # extensions. The minimum value is 50 (A setting below 50 will be treated
    # as 50).

    snapshot_autoextend_threshold = 100
    snapshot_autoextend_percent = 20

    # 'thin_pool_autoextend_threshold' and 'thin_pool_autoextend_percent' define
    # how to handle automatic pool extension. The former defines when the
    # pool should be extended: when its space usage exceeds this many
    # percent. The latter defines how much extra space should be allocated for
    # the pool, in percent of its current size.
    #
    # For example, if you set thin_pool_autoextend_threshold to 70 and
    # thin_pool_autoextend_percent to 20, whenever a pool exceeds 70% usage,
    # it will be extended by another 20%. For a 1G pool, using up 700M will
    # trigger a resize to 1.2G. When the usage exceeds 840M, the pool will
    # be extended to 1.44G, and so on.
    #
    # Setting thin_pool_autoextend_threshold to 100 disables automatic
    # extensions. The minimum value is 50 (A setting below 50 will be treated
    # as 50).

    thin_pool_autoextend_threshold = 100
    thin_pool_autoextend_percent = 20

    # Full path of the utility called to check that a thin metadata device
    # is in a state that allows it to be used.
    # Each time a thin pool needs to be activated, this utility is executed.
    # The activation will only proceed if the utility has an exit status of 0.
    # Set to "" to skip this check.  (Not recommended.)
    # The thin tools are available as part of the device-mapper-persistent-data
    # package from https://github.com/jthornber/thin-provisioning-tools.
    #
    thin_check_executable = "/usr/sbin/thin_check"

    # String with options passed with thin_check command. By default,
    # option '-q' is for quiet output.
    thin_check_options = [ "-q" ]

    # While activating devices, I/O to devices being (re)configured is
    # suspended, and as a precaution against deadlocks, LVM2 needs to pin
    # any memory it is using so it is not paged out.  Groups of pages that
    # are known not to be accessed during activation need not be pinned
    # into memory.  Each string listed in this setting is compared against
    # each line in /proc/self/maps, and the pages corresponding to any
    # lines that match are not pinned.  On some systems locale-archive was
    # found to make up over 80% of the memory used by the process.
    # mlock_filter = [ "locale/locale-archive", "gconv/gconv-modules.cache" ]

    # Set to 1 to revert to the default behaviour prior to version 2.02.62
    # which used mlockall() to pin the whole process's memory while activating
    # devices.
    use_mlockall = 0

    # Monitoring is enabled by default when activating logical volumes.
    # Set to 0 to disable monitoring or use the --ignoremonitoring option.
    monitoring = 1

    # When pvmove or lvconvert must wait for the kernel to finish
    # synchronising or merging data, they check and report progress
    # at intervals of this number of seconds.  The default is 15 seconds.
    # If this is set to 0 and there is only one thing to wait for, there
    # are no progress reports, but the process is awoken immediately the
    # operation is complete.
    polling_interval = 15
}


####################
# Advanced section #
####################

# Metadata settings
#
# metadata {
    # Default number of copies of metadata to hold on each PV.  0, 1 or 2.
    # You might want to override it from the command line with 0 
    # when running pvcreate on new PVs which are to be added to large VGs.

    # pvmetadatacopies = 1

    # Default number of copies of metadata to maintain for each VG.
    # If set to a non-zero value, LVM automatically chooses which of
    # the available metadata areas to use to achieve the requested
    # number of copies of the VG metadata.  If you set a value larger
    # than the the total number of metadata areas available then
    # metadata is stored in them all.
    # The default value of 0 ("unmanaged") disables this automatic
    # management and allows you to control which metadata areas
    # are used at the individual PV level using 'pvchange
    # --metadataignore y/n'.

    # vgmetadatacopies = 0

    # Approximate default size of on-disk metadata areas in sectors.
    # You should increase this if you have large volume groups or
    # you want to retain a large on-disk history of your metadata changes.

    # pvmetadatasize = 255

    # List of directories holding live copies of text format metadata.
    # These directories must not be on logical volumes!
    # It's possible to use LVM2 with a couple of directories here,
    # preferably on different (non-LV) filesystems, and with no other 
    # on-disk metadata (pvmetadatacopies = 0). Or this can be in
    # addition to on-disk metadata areas.
    # The feature was originally added to simplify testing and is not
    # supported under low memory situations - the machine could lock up.
    #
    # Never edit any files in these directories by hand unless you
    # you are absolutely sure you know what you are doing! Use
    # the supplied toolset to make changes (e.g. vgcfgrestore).

    # dirs = [ "/etc/lvm/metadata", "/mnt/disk2/lvm/metadata2" ]
#}

# Event daemon
#
dmeventd {
    # mirror_library is the library used when monitoring a mirror device.
    #
    # "libdevmapper-event-lvm2mirror.so" attempts to recover from
    # failures.  It removes failed devices from a volume group and
    # reconfigures a mirror as necessary. If no mirror library is
    # provided, mirrors are not monitored through dmeventd.

    mirror_library = "libdevmapper-event-lvm2mirror.so"

    # snapshot_library is the library used when monitoring a snapshot device.
    #
    # "libdevmapper-event-lvm2snapshot.so" monitors the filling of
    # snapshots and emits a warning through syslog when the use of
    # the snapshot exceeds 80%. The warning is repeated when 85%, 90% and
    # 95% of the snapshot is filled.

    snapshot_library = "libdevmapper-event-lvm2snapshot.so"

    # thin_library is the library used when monitoring a thin device.
    #
    # "libdevmapper-event-lvm2thin.so" monitors the filling of
    # pool and emits a warning through syslog when the use of
    # the pool exceeds 80%. The warning is repeated when 85%, 90% and
    # 95% of the pool is filled.

    thin_library = "libdevmapper-event-lvm2thin.so"

    # Full path of the dmeventd binary.
    #
    # executable = "/sbin/dmeventd"
}
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Appendix C. LVM Object Tags
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An LVM tag is a word that can be used to group LVM2 objects of the same type together. Tags can be attached to objects such as physical volumes, volume groups, and logical volumes. Tags can be attached to hosts in a cluster configuration. Snapshots cannot be tagged.
Tags can be given on the command line in place of PV, VG or LV arguments. Tags should be prefixed with @ to avoid ambiguity. Each tag is expanded by replacing it with all objects possessing that tag which are of the type expected by its position on the command line.
LVM tags are strings using [A-Za-z0-9_+.-] of up to 128 characters. They cannot start with a hyphen.
Only objects in a volume group can be tagged. Physical volumes lose their tags if they are removed from a volume group; this is because tags are stored as part of the volume group metadata and that is deleted when a physical volume is removed. Snapshots cannot be tagged.
The following command lists all the logical volumes with the database tag. 
lvs @database
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The following command lists the currently active host tags. 
lvm tags
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C.1. Adding and Removing Object Tags
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To add or delete tags from physical volumes, use the --addtag or --deltag option of the pvchange command.
To add or delete tags from volume groups, use the --addtag or --deltag option of the vgchange or vgcreate commands.
To add or delete tags from logical volumes, use the --addtag or --deltag option of the lvchange or lvcreate commands.

C.2. Host Tags
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In a cluster configuration, you can define host tags in the configuration files. If you set hosttags = 1 in the tags section, a host tag is automatically defined using the machine's hostname. This allow you to use a common configuration file which can be replicated on all your machines so they hold identical copies of the file, but the behavior can differ between machines according to the hostname.
For information on the configuration files, see Appendix B, The LVM Configuration Files.
For each host tag, an extra configuration file is read if it exists: lvm_hosttag.conf. If that file defines new tags, then further configuration files will be appended to the list of files to read in.
For example, the following entry in the configuration file always defines tag1, and defines tag2 if the hostname is host1. 
tags { tag1 { }  tag2 { host_list = ["host1"] } }
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C.3. Controlling Activation with Tags
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You can specify in the configuration file that only certain logical volumes should be activated on that host. For example, the following entry acts as a filter for activation requests (such as vgchange -ay) and only activates vg1/lvol0 and any logical volumes or volume groups with the database tag in the metadata on that host. 
activation { volume_list = ["vg1/lvol0", "@database" ] }
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There is a special match "@*" that causes a match only if any metadata tag matches any host tag on that machine.
As another example, consider a situation where every machine in the cluster has the following entry in the configuration file: 
tags { hosttags = 1 }
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If you want to activate vg1/lvol2 only on host db2, do the following:
  1. Run lvchange --addtag @db2 vg1/lvol2 from any host in the cluster.
  2. Run lvchange -ay vg1/lvol2.
This solution involves storing hostnames inside the volume group metadata.

Appendix D. LVM Volume Group Metadata
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The configuration details of a volume group are referred to as the metadata. By default, an identical copy of the metadata is maintained in every metadata area in every physical volume within the volume group. LVM volume group metadata is stored as ASCII.
A metadata area is a circular buffer. New metadata is appended to the old metadata and then the pointer to the start of it is updated.
You can specify the size of the metadata area with the --metadatasize. option of the pvcreate command. The default size may be too small for volume groups that contain physical volumes and logical volumes that number in the hundreds.
If a volume group contains many physical volumes, having many redundant copies of the metadata is inefficient. It is possible to create a physical volume without any metadata copies by using the --metadatacopies 0 option of the pvcreate command. Once you have selected the number of metadata copies the physical volume will contain, you cannot change that at a later point. Selecting 0 copies can result in faster updates on configuration changes. Note, however, that at all times every volume group must contain at least one physical volume with a metadata area (unless you are using the advanced configuration settings that allow you to store volume group metadata in a file system). If you intend to split the volume group in the future, every volume group needs at least one metadata copy.
As of Red Hat Enterprise Linux 5.6, you can also control metadata storage on a physical volume by using the --metadataignore option of the pvcreate command. If metadata areas on a physical volume are ignored, LVM will not store metadata in the metadata areas present on this physical volume. Since metadata areas cannot be created or extended after logical volumes have been allocated on the device, it is recommended that you allocate a metadata area in case you need it in the future even if you do not want to store metadata on this device. You can then use this option to instruct LVM to ignore the metadata area.
As of Red Hat Enterprise Linux 5.6, you can determine the number of metadata copies at the volume group level with the --vgmetadatacopies option of the vgcreate command. For information on setting this value, see the vgcreate man page. You may find this option useful for volume groups containing large numbers of physical volumes with metadata, as you can use the option to minimize metadata read and write overhead.
If you use the vgsplit command to split a volume group, the volume group retains the existing volume groups value of vgmetadatacopies. You can use the vgchange command to change the value of vgmetadatacopies.

D.1. The Physical Volume Label
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By default, the pvcreate command places the physical volume label in the 2nd 512-byte sector. This label can optionally be placed in any of the first four sectors, since the LVM tools that scan for a physical volume label check the first 4 sectors. The physical volume label begins with the string LABELONE.
The physical volume label Contains:
  • Physical volume UUID
  • Size of block device in bytes
  • NULL-terminated list of data area locations
  • NULL-terminated lists of metadata area locations
Metadata locations are stored as offset and size (in bytes). There is room in the label for about 15 locations, but the LVM tools currently use 3: a single data area plus up to two metadata areas.

D.2. Metadata Contents
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The volume group metadata contains:
  • Information about how and when it was created
  • Information about the volume group:
The volume group information contains:
  • Name and unique id
  • A version number which is incremented whenever the metadata gets updated
  • Any properties: Read/Write? Resizeable?
  • Any administrative limit on the number of physical volumes and logical volumes it may contain
  • The extent size (in units of sectors which are defined as 512 bytes)
  • An unordered list of physical volumes making up the volume group, each with:
    • Its UUID, used to determine the block device containing it
    • Any properties, such as whether the physical volume is allocatable
    • The offset to the start of the first extent within the physical volume (in sectors)
    • The number of extents
  • An unordered list of logical volumes. each consisting of
    • An ordered list of logical volume segments. For each segment the metadata includes a mapping applied to an ordered list of physical volume segments or logical volume segments

D.3. Sample Metadata
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The following shows an example of LVM volume group metadata for a volume group called myvg. 
# Generated by LVM2: Tue Jan 30 16:28:15 2007

contents = "Text Format Volume Group"
version = 1

description = "Created *before* executing 'lvextend -L+5G /dev/myvg/mylv /dev/sdc'"

creation_host = "tng3-1"        # Linux tng3-1 2.6.18-8.el5 #1 SMP Fri Jan 26 14:15:21 EST 2007 i686
creation_time = 1170196095      # Tue Jan 30 16:28:15 2007

myvg {
        id = "0zd3UT-wbYT-lDHq-lMPs-EjoE-0o18-wL28X4"
        seqno = 3
        status = ["RESIZEABLE", "READ", "WRITE"]
        extent_size = 8192              # 4 Megabytes
        max_lv = 0
        max_pv = 0

        physical_volumes {

                pv0 {
                        id = "ZBW5qW-dXF2-0bGw-ZCad-2RlV-phwu-1c1RFt"
                        device = "/dev/sda"     # Hint only

                        status = ["ALLOCATABLE"]
                        dev_size = 35964301     # 17.1491 Gigabytes
                        pe_start = 384
                        pe_count = 4390 # 17.1484 Gigabytes
                }

                pv1 {
                        id = "ZHEZJW-MR64-D3QM-Rv7V-Hxsa-zU24-wztY19"
                        device = "/dev/sdb"     # Hint only

                        status = ["ALLOCATABLE"]
                        dev_size = 35964301     # 17.1491 Gigabytes
                        pe_start = 384
                        pe_count = 4390 # 17.1484 Gigabytes
                }

                pv2 {
                        id = "wCoG4p-55Ui-9tbp-VTEA-jO6s-RAVx-UREW0G"
                        device = "/dev/sdc"     # Hint only

                        status = ["ALLOCATABLE"]
                        dev_size = 35964301     # 17.1491 Gigabytes
                        pe_start = 384
                        pe_count = 4390 # 17.1484 Gigabytes
                }

                pv3 {
                        id = "hGlUwi-zsBg-39FF-do88-pHxY-8XA2-9WKIiA"
                        device = "/dev/sdd"     # Hint only

                        status = ["ALLOCATABLE"]
                        dev_size = 35964301     # 17.1491 Gigabytes
                        pe_start = 384
                        pe_count = 4390 # 17.1484 Gigabytes
                }
        }
        logical_volumes {

                mylv {
                        id = "GhUYSF-qVM3-rzQo-a6D2-o0aV-LQet-Ur9OF9"
                        status = ["READ", "WRITE", "VISIBLE"]
                        segment_count = 2

                        segment1 {
                                start_extent = 0
                                extent_count = 1280     # 5 Gigabytes

                                type = "striped"
                                stripe_count = 1        # linear

                                stripes = [
                                        "pv0", 0
                                ]
                        }
                        segment2 {
                                start_extent = 1280
                                extent_count = 1280     # 5 Gigabytes

                                type = "striped"
                                stripe_count = 1        # linear

                                stripes = [
                                        "pv1", 0
                                ]
                        }
                }
        }
}
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Appendix E. Revision History
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Revision History
Revision 8.0-8Mon Sep 8 2014Steven Levine
Version for 5.11 GA release
Revision 8.0-6Mon Jun 30 2014Steven Levine
Beta release of Red Hat Enterprise Linux 5.11
Revision 8.0-4Tue Jun 10 2014Steven Levine
Resolves: #1092639
Documents lvm tags command.
Resolves: #1092638
Updates documentation to reflect deprecation of major number.
Revision 8.0-0Fri May 2 2014Steven Levine
First draft for Red Hat Enterprise Linux 5.11
Revision 7.0-3Wed Jul 10 2013Steven Levine
Beta release of Red Hat Enterprise Linux 5.10
Revision 7.0-2Tue May 28 2013Steven Levine
Resolves: #796977
Adds section on LVM allocation policies.
Revision 7.0-1Thu May 23 2013Steven Levine
Adding new section on Allocation policies.
Revision 7.0-0Tue May 14 2013Steven Levine
Test printing for new Publican
Revision 6.0-7Fri Jan 4 2013Steven Levine
Version for Red Hat Enterprise Linux 5.9 GA release
Revision 6.0-6Mon Nov 19 2012Steven Levine
Resolves: #878152
Updates sample lvm.conf file in Appendix B to Red Hat Enterprise Linux 5.9 version.
Revision 6.0-5Wed Nov 7 2012Steven Levine
Resolves: #874159
Corrects small error in lvchange example.
Revision 6.0-4Thu Aug 30 2012Steven Levine
Beta release of Red Hat Enterprise Linux 5.9
Revision 6.0-1Tue Jul 31 2012Steven Levine
Resolves: #736548
Notes that clustered log daemon should be installed and running to perform pvmove in a cluster.
Resolves: #801525
Makes prompts consistent in all examples.
Revision 5.0-4Thu Feb 16 2012Steven Levine
Release for GA of Red Hat Enterprise Linux 5.8
Revision 5.0-3Thu Dec 15 2011Steven Levine
Beta release of Red Hat Enterprise Linux 5.8
Revision 5.0-2Tue Nov 23 2011Steven Levine
Resolves: #755739, #755734, #755736
Corrects and clarifies small issues found during QE review.
Revision 5.0-1Thu Nov 9 2011Steven Levine
Resolves: #742311
Documents the --nosync option of lvextend command in Red Hat Enterprise Linux 5.8.
Resolves: #736458
Indicates that cluster mirror packages should be installed to relocate a pv in a cluster.
Resolves: #730761
Removes outdated references.
Revision 4.0-1Thu Jul 21 2011Steven Levine
Resolves: #705139
Documents new LVM features supported in Red Hat Enterprise Linux release 5.7.
Resolves: #712437
Documents support of mirrored stripes in Red Hat Enterprise Linux release 5.7.
Resolves: #654898
Fixes minor typographical errors.
Revision 3.0-1Thu Dec 23 2010Steven Levine
Updates sample lvm.conf file for Red Hat Enterprise Linux 5.6 release.
Resolves: #531637
Adds note clarifying behavior of mirror log management when the device holding the cluster mirror log becomes unavailable.
Resolves: #659496
Documents new features: splitmirror, mirroring mirror log, and managing metadata, as described in New and Changed Features section.
Resolves: #637188
Removes outdated information that the pvmove command is not supported in a cluster.
Resolves: #656195
Corrects small typographic errors.
Revision 2.0-1Thu Mar 11 2010Steven Levine
Updates lvm.conf for Red Hat Enterprise Linux 5.5 release.
Resolves: #532588
Clarifies necessity for running vgscan when hardware configuration changes.
Revision 1.0-1Tue Aug 18 2009Steven Levine
Replaces Cluster Logical Volume Manager, resolving bugs against that document.
Resolves: #510273
Clarifies lack of snapshot support in clustered volume groups.
Resolves: #515742
Documents necessity for increasing mirror region size from default value for mirrors that are larger than 1.5TB.
Resolves: #491028
Fixes assorted wording and format errors.
Resolves: #491028
Fixes assorted wording and format errors.
Resolves: #504028
Provides new sections and documentation on creating mirrors in a cluster; general technical corrections.
Resolves: #494007
Clarifies description of setting snapshot size.
Resolves: #504028
Adds example showing creation of a mirrored volume in a cluster.
Resolves: #518567
Adds caution about ensuring all nodes in a cluster can access shared storage.
Resolves: #510920
Fixes typo.

Index
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A

activating logical volumes
individual nodes, Activating Logical Volumes on Individual Nodes in a Cluster
activating volume groups, Activating and Deactivating Volume Groups
individual nodes, Activating and Deactivating Volume Groups
local node only, Activating and Deactivating Volume Groups
administrative procedures, LVM Administration Overview
allocation, LVM Allocation
policy, Creating Volume Groups
preventing, Preventing Allocation on a Physical Volume
archive file, Logical Volume Backup, Backing Up Volume Group Metadata

B

backup
file, Logical Volume Backup
metadata, Logical Volume Backup, Backing Up Volume Group Metadata
backup file, Backing Up Volume Group Metadata
block device
scanning, Scanning for Block Devices

C

cache file
building, Scanning Disks for Volume Groups to Build the Cache File
cluster environment, The Clustered Logical Volume Manager (CLVM), Creating LVM Volumes in a Cluster
CLVM
definition, The Clustered Logical Volume Manager (CLVM)
clvmd daemon, The Clustered Logical Volume Manager (CLVM)
command line units, Using CLI Commands
configuration examples, LVM Configuration Examples
creating
logical volume, Creating Logical Volumes
logical volume, example, Creating an LVM Logical Volume on Three Disks
LVM volumes in a cluster, Creating LVM Volumes in a Cluster
physical volumes, Creating Physical Volumes
striped logical volume, example, Creating a Striped Logical Volume
volume group, clustered, Creating Volume Groups in a Cluster
volume groups, Creating Volume Groups
creating LVM volumes
overview, Logical Volume Creation Overview

D

data relocation, online, Online Data Relocation
deactivating volume groups, Activating and Deactivating Volume Groups
exclusive on one node, Activating and Deactivating Volume Groups
local node only, Activating and Deactivating Volume Groups
device numbers
major, Persistent Device Numbers
minor, Persistent Device Numbers
persistent, Persistent Device Numbers
device path names, Using CLI Commands
device scan filters, Controlling LVM Device Scans with Filters
device size, maximum, Creating Volume Groups
device special file directory, Creating Volume Groups
display
sorting output, Sorting LVM Reports
displaying
logical volumes, Displaying Logical Volumes, The lvs Command
physical volumes, Displaying Physical Volumes, The pvs Command
volume groups, Displaying Volume Groups, The vgs Command

E

extent
allocation, Creating Volume Groups, LVM Allocation
definition, Volume Groups, Creating Volume Groups

F

failed devices
displaying, Displaying Information on Failed Devices
features, new and changed, New and Changed Features
file system
growing on a logical volume, Growing a File System on a Logical Volume
filters, Controlling LVM Device Scans with Filters

G

growing file system
logical volume, Growing a File System on a Logical Volume

H

help display, Using CLI Commands

I

initializing
partitions, Initializing Physical Volumes
physical volumes, Initializing Physical Volumes
Insufficient Free Extents message, Insufficient Free Extents for a Logical Volume

L

linear logical volume
converting to mirrored, Changing Mirrored Volume Configuration
creation, Creating Linear Volumes
definition, Linear Volumes
logging, Logging
logical volume
administration, general, Logical Volume Administration
changing parameters, Changing the Parameters of a Logical Volume Group
creation, Creating Logical Volumes
creation example, Creating an LVM Logical Volume on Three Disks
definition, Logical Volumes, LVM Logical Volumes
displaying, Displaying Logical Volumes, Customized Reporting for LVM, The lvs Command
exclusive access, Activating Logical Volumes on Individual Nodes in a Cluster
extending, Growing Logical Volumes
growing, Growing Logical Volumes
linear, Creating Linear Volumes
local access, Activating Logical Volumes on Individual Nodes in a Cluster
lvs display arguments, The lvs Command
mirrored, Creating Mirrored Volumes
reducing, Shrinking Logical Volumes
removing, Removing Logical Volumes
renaming, Renaming Logical Volumes
resizing, Resizing Logical Volumes
shrinking, Shrinking Logical Volumes
snapshot, Creating Snapshot Volumes
striped, Creating Striped Volumes
lvchange command, Changing the Parameters of a Logical Volume Group
lvconvert command, Changing Mirrored Volume Configuration
lvcreate command, Creating Logical Volumes
lvdisplay command, Displaying Logical Volumes
lvextend command, Growing Logical Volumes
LVM
architecture overview, LVM Architecture Overview
clustered, The Clustered Logical Volume Manager (CLVM)
components, LVM Architecture Overview, LVM Components
custom report format, Customized Reporting for LVM
directory structure, Creating Volume Groups
help, Using CLI Commands
history, LVM Architecture Overview
label, Physical Volumes
logging, Logging
logical volume administration, Logical Volume Administration
physical volume administration, Physical Volume Administration
physical volume, definition, Physical Volumes
volume group, definition, Volume Groups
LVM1, LVM Architecture Overview
LVM2, LVM Architecture Overview
lvmdiskscan command, Scanning for Block Devices
lvreduce command, Resizing Logical Volumes, Shrinking Logical Volumes
lvremove command, Removing Logical Volumes
lvrename command, Renaming Logical Volumes
lvs command, Customized Reporting for LVM, The lvs Command
display arguments, The lvs Command
lvscan command, Displaying Logical Volumes

M

man page display, Using CLI Commands
metadata
backup, Logical Volume Backup, Backing Up Volume Group Metadata
recovery, Recovering Physical Volume Metadata
mirrored logical volume
clustered, Creating a Mirrored LVM Logical Volume in a Cluster
converting to linear, Changing Mirrored Volume Configuration
creation, Creating Mirrored Volumes
definition, Mirrored Logical Volumes
extending, Extending a Mirrored Volume
failure recovery, Recovering from LVM Mirror Failure
growing, Extending a Mirrored Volume
reconfiguration, Changing Mirrored Volume Configuration

O

online data relocation, Online Data Relocation
overview
features, new and changed, New and Changed Features

P

partition type, setting, Setting the Partition Type
partitions
multiple, Multiple Partitions on a Disk
path names, Using CLI Commands
persistent device numbers, Persistent Device Numbers
physical extent
preventing allocation, Preventing Allocation on a Physical Volume
physical volume
adding to a volume group, Adding Physical Volumes to a Volume Group
administration, general, Physical Volume Administration
creating, Creating Physical Volumes
definition, Physical Volumes
display, The pvs Command
displaying, Displaying Physical Volumes, Customized Reporting for LVM
illustration, LVM Physical Volume Layout
initializing, Initializing Physical Volumes
layout, LVM Physical Volume Layout
pvs display arguments, The pvs Command
recovery, Replacing a Missing Physical Volume
removing, Removing Physical Volumes
removing from volume group, Removing Physical Volumes from a Volume Group
removing lost volume, Removing Lost Physical Volumes from a Volume Group
resizing, Resizing a Physical Volume
pvdisplay command, Displaying Physical Volumes
pvmove command, Online Data Relocation
pvremove command, Removing Physical Volumes
pvresize command, Resizing a Physical Volume
pvs command, Customized Reporting for LVM
display arguments, The pvs Command
pvscan command, Displaying Physical Volumes

R

removing
disk from a logical volume, Removing a Disk from a Logical Volume
logical volume, Removing Logical Volumes
physical volumes, Removing Physical Volumes
renaming
logical volume, Renaming Logical Volumes
volume group, Renaming a Volume Group
report format, LVM devices, Customized Reporting for LVM
resizing
logical volume, Resizing Logical Volumes
physical volume, Resizing a Physical Volume

S

scanning
block devices, Scanning for Block Devices
scanning devices, filters, Controlling LVM Device Scans with Filters
snapshot logical volume
creation, Creating Snapshot Volumes
snapshot volume
definition, Snapshot Volumes
striped logical volume
creation, Creating Striped Volumes
creation example, Creating a Striped Logical Volume
definition, Striped Logical Volumes
extending, Extending a Striped Volume
growing, Extending a Striped Volume

T

troubleshooting, LVM Troubleshooting

U

units, command line, Using CLI Commands

V

verbose output, Using CLI Commands
vgcfbackup command, Backing Up Volume Group Metadata
vgcfrestore command, Backing Up Volume Group Metadata
vgchange command, Changing the Parameters of a Volume Group
vgcreate command, Creating Volume Groups, Creating Volume Groups in a Cluster
vgdisplay command, Displaying Volume Groups
vgexport command, Moving a Volume Group to Another System
vgextend command, Adding Physical Volumes to a Volume Group
vgimport command, Moving a Volume Group to Another System
vgmerge command, Combining Volume Groups
vgmknodes command, Recreating a Volume Group Directory
vgreduce command, Removing Physical Volumes from a Volume Group
vgrename command, Renaming a Volume Group
vgs command, Customized Reporting for LVM
display arguments, The vgs Command
vgscan command, Scanning Disks for Volume Groups to Build the Cache File
vgsplit command, Splitting a Volume Group
volume group
activating, Activating and Deactivating Volume Groups
administration, general, Volume Group Administration
changing parameters, Changing the Parameters of a Volume Group
combining, Combining Volume Groups
creating, Creating Volume Groups
creating in a cluster, Creating Volume Groups in a Cluster
deactivating, Activating and Deactivating Volume Groups
definition, Volume Groups
displaying, Displaying Volume Groups, Customized Reporting for LVM, The vgs Command
extending, Adding Physical Volumes to a Volume Group
growing, Adding Physical Volumes to a Volume Group
merging, Combining Volume Groups
moving between systems, Moving a Volume Group to Another System
reducing, Removing Physical Volumes from a Volume Group
removing, Removing Volume Groups
renaming, Renaming a Volume Group
shrinking, Removing Physical Volumes from a Volume Group
splitting, Splitting a Volume Group
example procedure, Splitting a Volume Group
vgs display arguments, The vgs Command

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