Red Hat SummitCluster Logical Volume Manager
Red Hat Enterprise Linux 4
LVM Administrator's Guide
Edition 1.0
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.
Introduction
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. 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 and GFS file system administration.
2. Software Versions
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| Software | Description |
|---|---|
|
RHEL4
|
refers to RHEL4 and higher
|
|
GFS
|
refers to GFS 6.1 and higher
|
3. Related Documentation
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For more information about using Red Hat Enterprise Linux, refer to the following resources:
- Red Hat Enterprise Linux Installation Guide — Provides information regarding installation of Red Hat Enterprise Linux.
- Red Hat Enterprise Linux Introduction to System Administration — Provides introductory information for new Red Hat Enterprise Linux system administrators.
- Red Hat Enterprise Linux System Administration Guide — Provides more detailed information about configuring Red Hat Enterprise Linux to suit your particular needs as a user.
- Red Hat Enterprise Linux Reference Guide — Provides detailed information suited for more experienced users to reference when needed, as opposed to step-by-step instructions.
- Red Hat Enterprise Linux Security Guide — Details the planning and the tools involved in creating a secured computing environment for the data center, workplace, and home.
For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux, refer to the following resources:
- Red Hat Cluster Suite Overview — Provides a high level overview of the Red Hat Cluster Suite.
- Configuring and Managing a Red Hat Cluster — Provides information about installing, configuring and managing Red Hat Cluster components.
- Global File System: Configuration and Administration — Provides information about installing, configuring, and maintaining Red Hat GFS (Red Hat Global File System).
- Using Device-Mapper Multipath — Provides information about using the Device-Mapper Multipath feature of Red Hat Enterprise Linux.
- Using GNBD with Global File System — Provides an overview on using Global Network Block Device (GNBD) with Red Hat GFS.
- Linux Virtual Server Administration — Provides information on configuring high-performance systems and services with the Linux Virtual Server (LVS).
- Red Hat Cluster Suite Release Notes — Provides information about the current release of Red Hat Cluster Suite.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML and PDF versions online at the following location:
4. Feedback
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If you spot a typo, or if you have thought of a way to make this manual better, we would love to hear from you. Please submit a report in Bugzilla (http://bugzilla.redhat.com/bugzilla/) against the component
rh-cs.
Be sure to mention the manual's identifier:
rh-clvm(EN)-4.8 (2009-05-14T12:46)
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By mentioning this manual's identifier, we know exactly which version of the guide you have.
If you have a suggestion for improving the documentation, try to be as specific as possible. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.
Chapter 1. The LVM Logical Volume Manager
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This chapter provides a high-level overview of the components of the Logical Volume Manager (LVM).
1.1. 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.
A logical volume provides storage virtualization. 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 capacityWhen using logical volumes, file systems can extend across multiple disks, since you can aggregate disks and partitions into a single logical volume.
- Resizeable storage poolsYou can extend logical volumes or reduce logical volumes in size with simple software commands, without reformatting and repartitioning the underlying disk devices.
- Online data relocationTo 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 namingLogical storage volumes can be managed in user-defined groups, which you can name according to your convenience.
- Disk stripingYou can create a logical volume that stripes data across two or more disks. This can dramatically increase throughput.
- Mirroring volumesLogical volumes provide a convenient way to configure a mirror for your data.
- Volume SnapshotsUsing 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.
1.2. LVM Architecture Overview
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For the RHEL 4 release of the Linux operating system, 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 1.1, “LVM Logical Volume Components” shows the components of a simple LVM logical volume:
Figure 1.1. LVM Logical Volume Components
For detailed information on the components of an LVM logical volume, see Chapter 2, LVM Components.
1.3. Running LVM in a Cluster
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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.
The
clmvd 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.
Figure 1.2, “CLVM Overview” shows a CLVM overview in a Red Hat cluster.
Figure 1.2. CLVM Overview
Logical volumes created with CLVM on shared storage are visible to all computers that have access to the shared storage.
CLVM allows a user to configure logical volumes on shared storage by locking access to physical storage while a logical volume is being configured. CLVM uses the locking services provided by the high availability symmetric infrastructure.
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. For information on configuring the lvm.conf file to support CLVM, see Section 3.1, “Creating LVM Volumes in a Cluster”.
You configure LVM volumes for use in a cluster with the standard set of LVM commands or the LVM graphical user interface, as described in Chapter 4, LVM Administration with CLI Commands and Chapter 7, LVM Administration with the LVM GUI.
For information on installing LVM in a Red Hat Cluster, see Configuring and Managing a Red Hat Cluster.
1.4. Document Overview
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This remainder of this document includes the following chapters:
- Chapter 2, LVM Components describes the components that make up an LVM logical volume.
- Chapter 3, LVM Administration Overview provides an overview of the basic steps you perform to configure LVM logical volumes, whether you are using the LVM Command Line Interface (CLI) commands or the LVM Graphical User Interface (GUI).
- Chapter 4, LVM Administration with CLI Commands summarizes the individual administrative tasks you can perform with the LVM CLI commands to create and maintain logical volumes.
- Chapter 5, LVM Configuration Examples provides a variety of LVM configuration examples.
- Chapter 6, LVM Troubleshooting provide instructions for troubleshooting a variety of LVM issues.
- Chapter 7, LVM Administration with the LVM GUI summarizes the operating of the LVM GUI.
- Appendix A, The Device Mapper describes the Device Mapper that LVM uses to map logical and physical volumes.
- Appendix B, The LVM Configuration Files describes the LVM configuration files.
- Appendix C, LVM Object Tags describes LVM object tags and host tags.
- Appendix D, LVM Volume Group Metadata describes LVM volume group metadata, and includes a sample copy of metadata for an LVM volume group.
Chapter 2. LVM Components
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This chapter describes the components of an LVM Logical volume.
2.1. 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.
2.1.1. LVM Physical Volume Layout
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Figure 2.1, “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.
Figure 2.1. Physical Volume layout
2.1.2. 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 convenienceIt 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 performanceLVM can not 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 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.
2.2. 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.
2.3. 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.
2.3.1. Linear Volumes
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A linear volume aggregates multiple 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 2.2, “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.
Figure 2.2. Extent Mapping
The physical volumes that make up a logical volume do not have to be the same size. Figure 2.3, “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 100 extents in size (400MB) and PV2 is 200 extents in size (800MB). 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.
Figure 2.3. Linear Volume with Unequal Physical Volumes
You can configure more than one linear logical volume of whatever size you desire from the pool of physical extents. Figure 2.4, “Multiple Logical Volumes” shows the same volume group as in Figure 2.3, “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).
Figure 2.4. Multiple Logical Volumes
2.3.2. 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-round 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 cannnot exceed the size of an extent.
Figure 2.5. 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 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 4.4.9, “Extending a Striped Volume”.
2.3.3. 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 2.6, “Mirrored Logical Volume” shows a mirrored logical volume with one mirror. In this configuration, the log is maintained on disk.
Figure 2.6. Mirrored Logical Volume
For information on creating and modifying mirrors, see Section 4.4.1.3, “Creating Mirrored Volumes”.
2.3.4. 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.
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
fsckcommand 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 3. 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 5, LVM Configuration Examples.
For descriptions of the CLI commands you can use to perform LVM administration, see Chapter 4, LVM Administration with CLI Commands. Alternately, you can use the LVM GUI, which is described in Chapter 7, LVM Administration with the LVM GUI.
3.1. Creating LVM Volumes in a Cluster
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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. Creating clustered logical volumes also requires changes to the
lvm.conf file for cluster-wide locking. Other than this setup, creating LVM logical volumes in a clustered 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 cluster-wide locking, you can run the
lvmconf command, as follows:
/usr/sbin/lvmconf --enable-cluster
# /usr/sbin/lvmconf --enable-cluster
Running the
lvmconf command modifies the lvm.conf file to specify the appropriate locking type for clustered volumes.
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 set up the cluster infrastructure, see Configuring and Managing a Red Hat Cluster.
For an example of creating a mirrored logical volume in a cluster, see Section 5.5, “Creating a Mirrored LVM Logical Volume in a Cluster”.
3.2. Logical Volume Creation Overview
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The following is a summary of the steps to perform to create an LVM logical volume.
- Initialize the partitions you will use for the LVM volume as physical volumes (this labels them).
- Create a volume group.
- 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.
- Create a GFS file system on the logical volume with the
gfs_mkfscommand. - Create a new mount point with the
mkdircommand. In a clustered system, create the mount point on all nodes in the cluster. - Mount the file system. You may want to add a line to the
fstabfile 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.
3.3. 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:
- Make a new physical volume.
- Extend the volume group that contains the logical volume with the file system you are growing to include the new physical volume.
- Extend the logical volume to include the new physical volume.
- 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.
3.4. 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 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 4.3.11, “Backing Up Volume Group Metadata”.
3.5. 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.
Chapter 4. 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 see Section 3.1, “Creating LVM Volumes in a Cluster”.
4.1. 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
# lvcreate -L 50MB new_vg
Rounding up size to full physical extent 52.00 MB
Logical volume "lvol0" created
The following command shows the output of the
lvcreate command with the -v argument.
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.
You can display help for any of the LVM CLI commands with the
--help argument of the command.
commandname --help
commandname --help
To display the man page for a command, execute the
man command:
man commandname
man commandname
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 see Section 6.4, “Recovering Physical Volume Metadata”.
4.2. Physical Volume Administration
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This section describes the commands that perform the various aspects of physical volume administration.
4.2.1. Creating Physical Volumes
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The following subsections describe the commands used for creating physical volumes.
4.2.1.1. 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
dd if=/dev/zero of=PhysicalVolume bs=512 count=1
4.2.1.2. 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/sdd1, /dev/sde1, and /dev/sdf1 for use as LVM physical volumes.
pvcreate /dev/sdd1 /dev/sde1 /dev/sdf1
pvcreate /dev/sdd1 /dev/sde1 /dev/sdf1
To initialize partitions rather than whole disks: run the
pvcreate command on the partition. The following example initializes /dev/hdb1 as an LVM physical volume for later use as part of an LVM logical volume.
pvcreate /dev/hdb1
pvcreate /dev/hdb1
4.2.1.3. 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.
4.2.2. 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 4.9, “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.
The
pvscan command scans all supported LVM block devices in the system for physical volumes.
The following command shows all physical devices found:
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 4.6, “Controlling LVM Device Scans with Filters”.
4.2.3. 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
pvchange -x n /dev/sdk1
You can also use the
-xy arguments of the pvchange command to allow allocation where it had previously been disallowed.
4.2.4. 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.
4.2.5. 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 4.3.5, “Removing Physical Volumes from a Volume Group”.
pvremove /dev/ram15
# pvremove /dev/ram15
Labels on physical volume "/dev/ram15" successfully wiped
4.3. Volume Group Administration
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This section describes the commands that perform the various aspects of volume group administration.
4.3.1. 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
vgcreate vg1 /dev/sdd1 /dev/sde1
When physical volumes are used to create a volume group, its disk space is divided into 4MB 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.
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/
/dev/vg/lv/
For example, if you create two volume groups
myvg1 and myvg2, each with three logical volumes named lvo1, lvo2, and lvo3, this create six device special files:
The maximum device size with LVM is 8 Exabytes on 64-bit CPUs.
4.3.2. 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
vgextend vg1 /dev/sdf1
4.3.3. 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 4.3.4, “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 4.9, “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.
4.3.4. Scanning Disks for Volume Groups to Build the Cache File
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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. You may need to run the vgscan command manually when you change your hardware configuration, 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 4.6, “Controlling LVM Device Scans with Filters”.
The following example shows the output of a
vgscan command.
vgscan
# 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
4.3.5. Removing Physical Volumes from a Volume Group
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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.
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
# vgreduce my_volume_group /dev/hda14.3.6. 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 4.3.7, “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
vgchange -l 128 /dev/vg00
For a description of the volume group parameters you can change with the
vgchange command, see the vgchange(8) man page.
4.3.7. 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 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
vgchange -a n my_volume_group
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 4.4.4, “Changing the Parameters of a Logical Volume Group”, For information on activating logical volumes on individual nodes in a cluster, see Section 4.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
4.3.8. Removing Volume Groups
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To remove a volume group that contains no logical volumes, use the
vgremove command.
vgremove officevg
# vgremove officevg
Volume group "officevg" successfully removed
4.3.9. 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
# vgsplit bigvg smallvg /dev/ram15
Volume group "smallvg" successfully split from "bigvg"
4.3.10. Combining Volume Groups
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Two 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
vgmerge -v databases my_vg
4.3.11. 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 6.4, “Recovering Physical Volume Metadata”.
4.3.12. 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
vgrename /dev/vg02 /dev/my_volume_group
vgrename vg02 my_volume_group
vgrename vg02 my_volume_group
4.3.13. 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:
- Make sure that no users are accessing files on the active volumes in the volume group, then unmount the logical volumes.
- Use the
-a nargument of thevgchangecommand to mark the volume group as inactive, which prevents any further activity on the volume group. - Use the
vgexportcommand 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 thepvscancommand, as in the following example.Copy to Clipboard Copied! Toggle word wrap Toggle overflow When the system is next shut down, you can unplug the disks that constitute the volume group and connect them to the new system. - When the disks are plugged into the new system, use the
vgimportcommand to import the volume group, making it accessible to the new system. - Activate the volume group with the
-a yargument of thevgchangecommand. - Mount the file system to make it available for use.
4.3.14. 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 and removes unused ones.
You can incorporate the
vgmknodes command into the vgscan command by specifying the mknodes argument to the vgscan command.
4.4. Logical Volume Administration
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This section describes the commands that perform the various aspects of logical volume administration.
4.4.1. 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.
4.4.1.1. 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
lvcreate -L 10G vg1
The following command creates a 1500 megabyte linear logical volume named
testlv in the volume group testvg, creating the block device /dev/testvg/testlv.
lvcreate -L1500 -ntestlv testvg
lvcreate -L1500 -ntestlv testvg
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
lvcreate -L 50G -n gfslv vg0
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 testvol.
lvcreate -l 60%VG -n mylv testvg
lvcreate -l 60%VG -n mylv testvg
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 testvol.
lvcreate -l 100%FREE -n yourlv testvg
lvcreate -l 100%FREE -n yourlv testvg
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 the lvcreate command.
The following commands create a logical volume called
mylv that fills the volume group named testvg.
vgdisplay testvg | grep "Total PE" lvcreate -l 10230 testvg -n mylv
# vgdisplay testvg | grep "Total PE"
Total PE 10230
# lvcreate -l 10230 testvg -n mylv
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 4.3.5, “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
lvcreate -L 1500 -ntestlv testvg /dev/sdg1
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 25 of physical volume
/dev/sda1 and extents 50 through 125 of physical volume /dev/sdb1 in volume group testvg.
lvcreate -l 100 -n testlv testvg /dev/sda1:0-25 /dev/sdb1:50-125
lvcreate -l 100 -n testlv testvg /dev/sda1:0-25 /dev/sdb1:50-125
The following example creates a linear logical volume out of extents 0 through 25 of physical volume
/dev/sda1 and then continues laying out the logical volume at extent 100.
lvcreate -l 100 -n testlv testvg /dev/sda1:0-25:100-
lvcreate -l 100 -n testlv testvg /dev/sda1:0-25:100-
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 4.3.1, “Creating Volume Groups”.
4.4.1.2. 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 2.3.2, “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).
The stripe size should be tuned to a power of 2 between 4kB and 512kB, and matched to the application's I/O that is using the striped volume. The
-I argument of the lvcreate command specifies the stripe size in kilobytes.
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
lvcreate -L 50G -i2 -I64 -n gfslv vg0
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 0-50 of /dev/sda1 and sectors 50-100 of /dev/sdb1.
lvcreate -l 100 -i2 -nstripelv testvg /dev/sda1:0-50 /dev/sdb1:50-100
# lvcreate -l 100 -i2 -nstripelv testvg /dev/sda1:0-50 /dev/sdb1:50-100
Using default stripesize 64.00 KB
Logical volume "stripelv" created
4.4.1.3. Creating Mirrored Volumes
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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
lvcreate -L 50G -m1 -n mirrorlv vg0
An LVM mirror divides the device being copied into regions that, by default, are 512KB in size. You can use the
-R argument to specify the region size in MB. 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 12MB in size and keeps the mirror log in memory.
lvcreate -L 12MB -m1 --corelog -n ondiskmirvol bigvg
# lvcreate -L 12MB -m1 --corelog -n ondiskmirvol bigvg
Logical volume "ondiskmirvol" created
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.
You can specify which devices to use for the mirror logs 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 megabytes 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
lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1 /dev/sdb1 /dev/sdc1
The following command creates a mirrored logical volume with a single mirror. The volume is 500 megabytes 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 1MB 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
lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1:0-499 /dev/sdb1:0-499 /dev/sdc1:0
Note
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 5.5, “Creating a Mirrored LVM Logical Volume in a Cluster”.
4.4.1.4. 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 6.3, “Recovering from LVM Mirror Failure”.
The following command converts the linear logical volume
vg00/lvol1 to a mirrored logical volume.
lvconvert -m1 vg00/lvol1
lvconvert -m1 vg00/lvol1
The following command converts the mirrored logical volume
vg00/lvol1 to a linear logical volume, removing the mirror leg.
lvconvert -m0 vg00/lvol1
lvconvert -m0 vg00/lvol1
4.4.2. 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 (major and minor) number. You can specify these with the
lvcreate and the lvchange commands by using the following arguments:
--persistent y --major major --minor minor
--persistent y --major major --minor minor
Use a large minor number to be sure that it hasn't 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.
4.4.3. 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
lvreduce -l -3 vg00/lvol1
4.4.4. Changing the Parameters of a Logical Volume Group
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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 4.3.6, “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
lvchange -pr vg00/lvol1
4.4.5. 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
lvrename /dev/vg02/lvold /dev/vg02/lvnew
lvrename vg02 lvold lvnew
lvrename vg02 lvold lvnew
For more information on activating logical volumes on individual nodes in a cluster, see Section 4.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
4.4.6. Removing Logical Volumes
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To remove an inactive logical volume, use the
lvremove command. If the logical volume is currently mounted, you must close the volume with the umount command 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
[root@tng3-1 lvm]# lvremove /dev/testvg/testlv
Do you really want to remove active logical volume "testlv"? [y/n]: y
Logical volume "testlv" successfully removed
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.
4.4.7. 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 4.9, “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
lvdisplay -v /dev/vg00/lvol2
The
lvscan command scans for all logical volumes in the system and lists them, as in the following example.
lvscan
# lvscan
ACTIVE '/dev/vg0/gfslv' [1.46 GB] inherit
4.4.8. 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 volumne
/dev/myvg/homevol to 12 gigabytes.
lvextend -L12G /dev/myvg/homevol
# 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
The following command adds another gigabyte to the logical volume
/dev/myvg/homevol.
lvextend -L+1G /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
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
[root@tng3-1 ~]# lvextend -l +100%FREE /dev/myvg/testlv
Extending logical volume testlv to 68.59 GB
Logical volume testlv successfully resized
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.
4.4.9. 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
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 2 0 0 wz--n- 271.31G 271.31G
You can create a stripe using the entire amount of space in the volume group.
Note that the volume group now has no more free space.
vgs
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 2 1 0 wz--n- 271.31G 0
The following command adds another physical volume to the volume group, which then has 135G of additional space.
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.
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.
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.
4.4.10. 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
lvreduce -l -3 vg00/lvol1
4.5. Creating Snapshot Volumes
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Use the
-s argument of the lvcreate command to create a snapshot volume. A snapshot volume is writeable.
LVM snapshots are not cluster-aware, so they require exclusive access to a volume. For information on activating logical volumes on individual nodes in a cluster, see Section 4.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
The following command creates a snapshot logical volume that is 100 megabytes 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
lvcreate --size 100M --snapshot --name snap /dev/vg00/lvol1
After you create a snapshot logical volume, specifying the origin volume on the
lvdisplay command yields output that includes a 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.
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
# 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
Note
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.
4.6. 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 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/.*/" ]
filter = [ "a/.*/" ]
The following filter removes the cdrom device in order to avoid delays if the drive contains no media:
filter = [ "r|/dev/cdrom|" ]
filter = [ "r|/dev/cdrom|" ]
The following filter adds all loop and removes all other block devices:
filter = [ "a/loop.*/", "r/.*/" ]
filter = [ "a/loop.*/", "r/.*/" ]
The following filter adds all loop and IDE and removes all other block devices:
filter =[ "a|loop.*|", "a|/dev/hd.*|", "r|.*|" ]
filter =[ "a|loop.*|", "a|/dev/hd.*|", "r|.*|" ]
The following filter adds just partition 8 on the first IDE drive and removes all other block devices:
filter = [ "a|^/dev/hda8$|", "r/.*/" ]
filter = [ "a|^/dev/hda8$|", "r/.*/" ]
For more information on the
lvm.conf file, see Appendix B, The LVM Configuration Files and the lvm.conf(5) man page.
4.7. 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.
Because the
pvmove command uses mirroring, it is not cluster-aware and needs exclusive access to a volume. For information on activating logical volumes on individual nodes in a cluster, see Section 4.8, “Activating Logical Volumes on Individual Nodes in a Cluster”.
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
pvmove /dev/sdc1
The following command moves just the extents of the logical volume
MyLV.
pvmove -n MyLV /dev/sdc1
pvmove -n MyLV /dev/sdc1
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 to the physical volume /dev/sdc1 over to /dev/sdf1 in the background.
pvmove -b /dev/sdc1 /dev/sdf1
pvmove -b /dev/sdc1 /dev/sdf1
The following command reports the progress of the move as a percentage at five second intervals.
pvmove -i5 /dev/sdd1
pvmove -i5 /dev/sdd1
4.8. Activating Logical Volumes on Individual Nodes in a Cluster
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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. For example, the
pvmove command is not cluster-aware and needs exclusive access to a volume. LVM snapshots require exclusive access to a volume as well.
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.
4.9. 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.
4.9.1. 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
-oargument. For example, the following output is the default display for thepvscommand (which displays information about physcial volumes).Copy to Clipboard Copied! Toggle word wrap Toggle overflow The following command displays only the physical volume name and size.Copy to Clipboard Copied! Toggle word wrap Toggle overflow - 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.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Adding the
-vargument to a command includes some extra fields. For example, thepvs -vcommand will display theDevSizeandPV UUIDfields in addition to the default fields.Copy to Clipboard Copied! Toggle word wrap Toggle overflow - The
--noheadingsargument suppresses the headings line. This can be useful for writing scripts.The following example uses the--noheadingsargument in combination with thepv_nameargument, which will generate a list of all physical volumes.pvs --noheadings -o pv_name
# pvs --noheadings -o pv_name /dev/sdb1 /dev/sdc1 /dev/sdd1Copy to Clipboard Copied! Toggle word wrap Toggle overflow - The
--separator separatorargument uses separator to separate each field.The following example separates the default output fields of thepvscommand with an equals sign (=).Copy to Clipboard Copied! Toggle word wrap Toggle overflow To keep the fields aligned when using theseparatorargument, use theseparatorargument in conjunction with the--alignedargument.Copy to Clipboard Copied! Toggle word wrap Toggle overflow
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 6.2, “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.
4.9.2. 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.
The pvs Command
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Table 4.1, “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.
| Argument | Header | Description |
|---|---|---|
dev_size | DevSize | The size of the underlying device on which the physical volume was created |
pe_start | 1st PE | Offset to the start of the first physical extent in the underlying device |
pv_attr | Attr | Status of the physical volume: (a)llocatable or e(x)ported. |
pv_fmt | Fmt | The metadata format of the physical volume (lvm2 or lvm1) |
pv_free | PFree | The free space remaining on the physical volume |
pv_name | PV | The physical volume name |
pv_pe_alloc_count | Alloc | Number of used physical extents |
pv_pe_count | PE | Number of physical extents |
pvseg_size | SSize | The segment size of the physical volume |
pvseg_start | Start | The starting physical extent of the physical volume segment |
pv_size | PSize | The size of the physical volume |
pv_tags | PV Tags | LVM tags attached to the physical volume |
pv_used | Used | The amount of space currently used on the physical volume |
pv_uuid | PV 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.
Using the
-v argument with the pvs command adds the following fields to the default display: dev_size, pv_uuid.
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.
You can use the
pvs -a command to see devices detected by LVM that have not been initialized as LVM physical volumes.
The vgs Command
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Table 4.2, “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.
| Argument | Header | Description |
|---|---|---|
lv_count | #LV | The number of logical volumes the volume group contains |
max_lv | MaxLV | The maximum number of logical volumes allowed in the volume group (0 if unlimited) |
max_pv | MaxPV | 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_attr | Attr | 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_size | Ext | The size of the physical extents in the volume group |
vg_fmt | Fmt | The metadata format of the volume group (lvm2 or lvm1) |
vg_free | VFree | Size of the free space remaining in the volume group |
vg_free_count | Free | Number of free physical extents in the volume group |
vg_name | VG | The volume group name |
vg_seqno | Seq | Number representing the revision of the volume group |
vg_size | VSize | The size of the volume group |
vg_sysid | SYS ID | LVM1 System ID |
vg_tags | VG Tags | LVM tags attached to the volume group |
vg_uuid | VG 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
# vgs
VG #PV #LV #SN Attr VSize VFree
new_vg 3 1 1 wz--n- 51.42G 51.36G
Using the
-v argument with the vgs command adds the following fields to the default display: vg_extent_size, vg_uuid.
The lvs Command
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Table 4.3, “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.
| Argument | Header | Description | ||||||
|---|---|---|---|---|---|---|---|---|
| Chunk | Unit size in a snapshot volume | ||||||
copy_percent | Copy% | The synchronization percentage of a mirrored logical volume; also used when physical extents are being moved with the pv_move command | ||||||
devices | Devices | The underlying devices that make up the logical volume: the physical volumes, logical volumes, and start physical extents and logical extents | ||||||
lv_attr | Attr | The status of the logical volume. The logical volume attribute bits are as follows:
| ||||||
lv_kernel_major | KMaj | Actual major device number of the logical volume (-1 if inactive) | ||||||
lv_kernel_minor | KMIN | Actual minor device number of the logical volume (-1 if inactive) | ||||||
lv_major | Maj | The persistent major device number of the logical volume (-1 if not specified) | ||||||
lv_minor | Min | The persistent minor device number of the logical volume (-1 if not specified) | ||||||
lv_name | LV | The name of the logical volume | ||||||
lv_size | LSize | The size of the logical volume | ||||||
lv_tags | LV Tags | LVM tags attached to the logical volume | ||||||
lv_uuid | LV UUID | The UUID of the logical volume. | ||||||
mirror_log | Log | Device on which the mirror log resides | ||||||
modules | Modules | Corresponding kernel device-mapper target necessary to use this logical volume | ||||||
move_pv | Move | Source physical volume of a temporary logical volume created with the pvmove command | ||||||
origin | Origin | The origin device of a snapshot volume | ||||||
| Region | The unit size of a mirrored logical volume | ||||||
seg_count | #Seg | The number of segments in the logical volume | ||||||
seg_size | SSize | The size of the segments in the logical volume | ||||||
seg_start | Start | Offset of the segment in the logical volume | ||||||
seg_tags | Seg Tags | LVM tags attached to the segments of the logical volume | ||||||
segtype | Type | The segment type of a logical volume (for example: mirror, striped, linear) | ||||||
snap_percent | Snap% | Current percentage of a snapshot volume that is in use | ||||||
stripes | #Str | Number of stripes or mirrors in a logical volume | ||||||
| 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. The default display is sorted by vg_name and lv_name within the volume group.
lvs
# 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
Using the
-v argauament 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.
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.
Using the
-v argument with the lvs --segments command adds the following fields to the default display: seg_start, stripesize, chunksize.
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.
4.9.3. 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.
The following example shows the same output, sorted by the free space field.
The following example shows that you do not need to display the field on which you are sorting.
To display a reverse sort, precede a field you specify after the
-O argument with the - character.
4.9.4. 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.
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.
The following command displays the output as a multiple of 1000.
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.
The following example displays the output of the
pvs command in units of 4 megabytes.
Chapter 5. LVM Configuration Examples
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This chapter provides some basic LVM configuration examples.
5.1. 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.
5.1.1. 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
[root@tng3-1 ~]# 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
5.1.2. 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
[root@tng3-1 ~]# vgcreate new_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1
Volume group "new_vol_group" successfully created
You can use the
vgs command to display the attributes of the new volume group.
vgs
[root@tng3-1 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
new_vol_group 3 0 0 wz--n- 51.45G 51.45G
5.1.3. 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
[root@tng3-1 ~]# lvcreate -L2G -n new_logical_volume new_vol_group
Logical volume "new_logical_volume" created
5.1.4. Creating the File System
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The following command creates a GFS file system on the logical volume.
The following commands mount the logical volume and report the file system disk space usage.
5.2. 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.
5.2.1. 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
[root@tng3-1 ~]# 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
5.2.2. Creating the Volume Group
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The following command creates the volume group
striped_vol_group.
vgcreate striped_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1
[root@tng3-1 ~]# vgcreate striped_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1
Volume group "striped_vol_group" successfully created
You can use the
vgs command to display the attributes of the new volume group.
vgs
[root@tng3-1 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
striped_vol_group 3 0 0 wz--n- 51.45G 51.45G
5.2.3. Creating the Logical Volume
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The following command creates the striped logical volume
striped_logical_volume from the volume group striped_vol_group. 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 striped_vol_group
[root@tng3-1 ~]# lvcreate -i3 -I4 -L2G -nstriped_logical_volume striped_vol_group
Rounding size (512 extents) up to stripe boundary size (513 extents)
Logical volume "striped_logical_volume" created
5.2.4. Creating the File System
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The following command creates a GFS file system on the logical volume.
The following commands mount the logical volume and report the file system disk space usage.
5.3. 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.
5.3.1. 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.
5.3.2. 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.
After moving the data, you can see that all of the space on
/dev/sdc1 is free.
5.3.3. 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
[root@tng3-1 ~]# lvchange -a n /dev/myvg/mylv
[root@tng3-1 ~]# vgsplit myvg yourvg /dev/sdc1
Volume group "yourvg" successfully split from "myvg"
You can use the
vgs command to see the attributes of the two volume groups.
vgs
[root@tng3-1 ~]# 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
5.3.4. 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
[root@tng3-1 ~]# lvcreate -L5G -n yourlv yourvg
Logical volume "yourlv" created
5.3.5. Making a File System and Mounting the New Logical Volume
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You can make a file system on the new logical volume and mount it.
5.3.6. Activating and Mounting the Original Logical Volume
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Since you had to deactivate the logical volume
mylv, you need to activate it again before you can mount it.
5.4. 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.
5.4.1. 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.
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.
After the
pvmove command has finished executing, the distribution of extents is as follows:
Use the
vgreduce command to remove the physical volume /dev/sdb1 from the volume group.
The disk can now be physically removed or allocated to other users.
5.4.2. 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:
We want to move the extents of
/dev/sdb1 to a new device, /dev/sdd1.
5.4.2.1. Creating the New Physical Volume
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Create a new physical volume from
/dev/sdd1.
pvcreate /dev/sdd1
[root@tng3-1 ~]# pvcreate /dev/sdd1
Physical volume "/dev/sdd1" successfully created
5.4.2.2. Adding the New Physical Volume to the Volume Group
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Add
/dev/sdd1 to the existing volume group myvg.
5.4.2.3. Moving the Data
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Use the
pvmove command to move the data from /dev/sdb1 to /dev/sdd1.
5.4.2.4. Removing the Old Physical Volume from the Volume Group
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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
[root@tng3-1 ~]# vgreduce myvg /dev/sdb1
Removed "/dev/sdb1" from volume group "myvg"
You can now reallocate the disk to another volume group or remove the disk from the system.
5.5. Creating a Mirrored LVM Logical Volume in a Cluster
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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 3.1, “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.
- 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.conffile 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
# /usr/sbin/lvmconf --enable-clusterCopy to Clipboard Copied! Toggle word wrap Toggle overflow - 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
clvmddaemon is running on the node from which it was issued:ps auxw | grep clvmd
[root@doc-07 ~]# ps auxw | grep clvmd root 17642 0.0 0.1 32164 1072 ? Ssl Apr06 0:00 clvmd -T20 -t 90Copy to Clipboard Copied! Toggle word wrap Toggle overflow The following command shows the local view of the cluster status:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Ensure that the
cmirrorandcmirror-kernelpackages are installed. Thecmirror-kernelpackage that must be installed depends on the kernel that is running. For example, if the running kernel iskernel-largesmp, it is necessary to havecmirror-kernel-largesmpfor the corresponding kernel version. - Start the
cmirrorservice.service cmirror start
[root@doc-07 ~]# service cmirror start Loading clustered mirror log: [ OK ]Copy to Clipboard Copied! Toggle word wrap Toggle overflow - 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.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow - Create the volume group. This example creates a volume group
mirrorvgthat consists of the three physical volumes that were created in the previous step.vgcreate mirrorvg /dev/xvdb1 /dev/xvdb2 /dev/xvdc1
[root@doc-07 ~]# vgcreate mirrorvg /dev/xvdb1 /dev/xvdb2 /dev/xvdc1 Clustered volume group "mirrorvg" successfully createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow Note that the output of thevgcreatecommand indicates that the volume group is clustered. You can verify that a volume group is clustered with thevgscommand, which will show the volume group's attributes. If a volume group is clustered, it will show a c attribute.vgs mirrorvg
[root@doc-07 ~]# vgs mirrorvg VG #PV #LV #SN Attr VSize VFree mirrorvg 3 0 0 wz--nc 68.97G 68.97GCopy to Clipboard Copied! Toggle word wrap Toggle overflow - Create the mirrored logical volume. This example creates the logical volume
mirrorlvfrom the volume groupmirrorvg. 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 mirrorvg -n mirrorlv /dev/xvdb1:1-1000 /dev/xvdb2:1-1000 /dev/xvdc1:0
[root@doc-07 ~]# lvcreate -l 1000 -m1 mirrorvg -n mirrorlv /dev/xvdb1:1-1000 /dev/xvdb2:1-1000 /dev/xvdc1:0 Logical volume "mirrorlv" createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow You can use thelvscommand 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.Copy to Clipboard Copied! Toggle word wrap Toggle overflow The completion of the mirror is noted in the system log:May 10 14:52:52 doc-07 [19402]: Monitoring mirror device mirrorvg-mirrorlv for events May 10 14:55:00 doc-07 lvm[19402]: mirrorvg-mirrorlv is now in-sync
May 10 14:52:52 doc-07 [19402]: Monitoring mirror device mirrorvg-mirrorlv for events May 10 14:55:00 doc-07 lvm[19402]: mirrorvg-mirrorlv is now in-syncCopy to Clipboard Copied! Toggle word wrap Toggle overflow - You can use the
lvswith the-o +devicesoptions 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.Copy to Clipboard Copied! Toggle word wrap Toggle overflow For release RHEL 4.8 and later, you can use theseg_pe_rangesoption of thelvsto display the data layout. You can use this option to verify that your layout is properly redundant. The output of this command dispays PE ranges in the same format that thelvcreateandlvresizecommands take as input.Copy to Clipboard Copied! Toggle word wrap Toggle overflow When you create the mirrored volume, you create theclustered_logdlm space, which will contain the dlm logs for all mirrors.Copy to Clipboard Copied! Toggle word wrap Toggle overflow
Note
For information on recovering from the failure of one of the legs of an LVM mirrored volume, see Section 6.3, “Recovering from LVM Mirror Failure”.
Chapter 6. LVM Troubleshooting
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This chapter provide instructions for troubleshooting a variety of LVM issues.
6.1. 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-vvvvargument 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
-vvvvargument. 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
lvmdumpcommand, which provides an information dump for diagnostic purposes. For information, see thelvmdump(8) man page. - Execute the
lvs -v,pvs -aordmsetup info -ccommand for additional system information. - Examine the last backup of the metadata in the
/etc/lvm/backupfile and archived versions in the/etc/lvm/archivefile. - Check the current configuration information by running the
lvm dumpconfigcommand. - Check the
.cachefile in the/etc/lvmdirectory for a record of which devices have physical volumes on them.
6.2. 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
[root@link-07 tmp]# vgs -o +devices
Volume group "vg" not found
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.
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
[root@link-07 tmp]# lvs -a -o +devices
Volume group "vg" not found
Using the
-P argument shows the logical volumes that have failed.
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.
6.3. 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.
The following commands creates the volume group
vg and the mirrored volume groupfs.
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.
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
[root@link-08 ~]# dd if=/dev/zero of=/dev/vg/groupfs count=10
10+0 records in
10+0 records out
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.
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.
Next you extend the original volume group with the new physical volume.
Convert the linear volume back to its original mirrored state.
lvconvert -m 1 /dev/vg/groupfs /dev/sda1 /dev/sdb1 /dev/sdc1
[root@link-08 ~]# lvconvert -m 1 /dev/vg/groupfs /dev/sda1 /dev/sdb1 /dev/sdc1
Logical volume mirror converted.
You can use the
lvs command to verify that the mirror is restored.
6.4. 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.
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.
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 restorefile argument instructs the pvcreate command to make the new physical volume compatible with the old one on the volume group, ensuring that the 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
[root@link-07 backup]# pvcreate --uuid "FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk" --restorefile /etc/lvm/archive/VG_00050.vg /dev/sdh1
Physical volume "/dev/sdh1" successfully created
You can then use the
vgcfgrestore command to restore the volume group's metadata.
vgcfgrestore VG
[root@link-07 backup]# vgcfgrestore VG
Restored volume group VG
You can now display the logical volumes.
lvs -a -o +devices
[root@link-07 backup]# 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)
The following commands activate the volumes and display the active volumes.
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.
6.5. 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 6.4, “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.
6.6. Removing Lost Physical Volumes from a Volume Group
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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.
6.7. Insufficient Free Extents for a Logical Volume
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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
# vgdisplay
--- Volume group ---
...
Free PE / Size 8780 / 34.30 GB
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
[root@tng3-1 ~]# 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
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
# lvcreate -l8780 -n testlv testvg
This uses all the free extents in the volume group.
vgs -o +vg_free_count,vg_extent_count
# 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
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 4.4.1.1, “Creating Linear Volumes”.
Chapter 7. 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 availalbe 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 generic 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 user interface to the Device Mapper is the
ioctl system call.
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 provides linear mapping, striped mapping, and error mapping, amongst others. Two disks can be concatenated into one logical volume with a pair of linear mappings, one for each disk.
The
dmsetup command is a command line wrapper for communication with the Device Mapper. It provides complete access to the ioctl commands through the libdevmapper command. For general system information about LVM devices, you may find the dmsetup info command to be useful.
For information about the options and capabilities of the
dmsetup command, see the dmsetup(8) man page.
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 tiles 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, the default file for RHEL 4.8. Your configuration file may differ for different releases.
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
lvs @database
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"] } }
tags { tag1 { } tag2 { host_list = ["host1"] } }
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" ] }
activation { volume_list = ["vg1/lvol0", "@database" ] }
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 }
tags { hosttags = 1 }
If you want to activate
vg1/lvol2 only on host db2, do the following:
- Run
lvchange --addtag @db2 vg1/lvol2from any host in the cluster. - 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 small and stored as ASCII.
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.
The core metadata is stored in 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 metadata area with the
--metadatasize. option of the pvcreate command. The default size is too small for volume groups with many logical volumes or physical volumes.
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.
Appendix E. Revision History
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| Revision History | |||
|---|---|---|---|
| Revision 1.0-10.400 | 2013-10-31 | ||
| |||
| Revision 1.0-10 | 2012-07-18 | ||
| |||
| Revision 1.0-0 | Wed Apr 01 2009 | ||
|
| |||
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
- policy, Creating Volume Groups
- preventing, Preventing Allocation on a Physical Volume
- archive file, Logical Volume Backup, Backing Up Volume Group Metadata
B
- backup
- backup file, Backing Up Volume Group Metadata
- block device
- scanning, Scanning for Block Devices
C
- cache file
- cluster environment, Running LVM in a Cluster, Creating LVM Volumes in a Cluster
- CLVM
- definition, Running LVM in a Cluster
- clvmd daemon, Running LVM in a Cluster
- 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 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
- definition, Volume Groups, Creating Volume Groups
F
- failed devices
- displaying, Displaying Information on Failed Devices
- feedback, Feedback
- 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, Running LVM in a Cluster
- 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
- lvm.conf file, Running LVM in a Cluster, Creating LVM Volumes in a Cluster, Logical Volume Backup, Logging, Backing Up Volume Group Metadata, Creating Mirrored Volumes, The LVM Configuration Files, Sample lvm.conf File
- LVM1, LVM Architecture Overview
- LVM2, LVM Architecture Overview
- lvmconf command, Creating LVM Volumes in a Cluster
- 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
- mirrored logical volume
- clustered, Creating Mirrored Volumes, Creating a Mirrored LVM Logical Volume in a Cluster
- converting to linear, Changing Mirrored Volume Configuration
- creation, Creating Mirrored Volumes
- definition, Mirrored Logical Volumes
- failure recovery, Recovering from LVM Mirror Failure
- reconfiguration, Changing Mirrored Volume Configuration
O
- online data relocation, Online Data Relocation
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
- 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
- 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
Legal Notice
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Copyright © 2009 Red Hat Inc..
This document is licensed by Red Hat under the Creative Commons Attribution-ShareAlike 3.0 Unported License. If you distribute this document, or a modified version of it, you must provide attribution to Red Hat, Inc. and provide a link to the original. If the document is modified, all Red Hat trademarks must be removed.
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