Managing file systems
Creating, modifying, and administering file systems in Red Hat Enterprise Linux 8
Abstract
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Chapter 1. Overview of available file systems
Choosing the file system that is appropriate for your application is an important decision due to the large number of options available and the trade-offs involved.
The following sections describe the file systems that Red Hat Enterprise Linux 8 includes by default, and recommendations on the most suitable file system for your application.
1.1. Types of file systems
Red Hat Enterprise Linux 8 supports a variety of file systems (FS). Different types of file systems solve different kinds of problems, and their usage is application specific. At the most general level, available file systems can be grouped into the following major types:
Type | File system | Attributes and use cases |
---|---|---|
Disk or local FS | XFS | XFS is the default file system in RHEL. Red Hat recommends deploying XFS as your local file system unless there are specific reasons to do otherwise: for example, compatibility or corner cases around performance. |
ext4 | ext4 has the benefit of familiarity in Linux, having evolved from the older ext2 and ext3 file systems. In many cases, it rivals XFS on performance. Support limits for ext4 filesystem and file sizes are lower than those on XFS. | |
Network or client-and-server FS | NFS | Use NFS to share files between multiple systems on the same network. |
SMB | Use SMB for file sharing with Microsoft Windows systems. | |
Shared storage or shared disk FS | GFS2 | GFS2 provides shared write access to members of a compute cluster. The emphasis is on stability and reliability, with the functional experience of a local file system as possible. SAS Grid, Tibco MQ, IBM Websphere MQ, and Red Hat Active MQ have been deployed successfully on GFS2. |
Volume-managing FS | Stratis (Technology Preview) | Stratis is a volume manager built on a combination of XFS and LVM. The purpose of Stratis is to emulate capabilities offered by volume-managing file systems like Btrfs and ZFS. It is possible to build this stack manually, but Stratis reduces configuration complexity, implements best practices, and consolidates error information. |
1.2. Local file systems
Local file systems are file systems that run on a single, local server and are directly attached to storage.
For example, a local file system is the only choice for internal SATA or SAS disks, and is used when your server has internal hardware RAID controllers with local drives. Local file systems are also the most common file systems used on SAN attached storage when the device exported on the SAN is not shared.
All local file systems are POSIX-compliant and are fully compatible with all supported Red Hat Enterprise Linux releases. POSIX-compliant file systems provide support for a well-defined set of system calls, such as read()
, write()
, and seek()
.
When considering a file system choice, choose a file system based on how large the file system needs to be, what unique features it must have, and how it performs under your workload.
- Available local file systems
- XFS
- ext4
1.3. The XFS file system
XFS is a highly scalable, high-performance, robust, and mature 64-bit journaling file system that supports very large files and file systems on a single host. It is the default file system in Red Hat Enterprise Linux 8. XFS was originally developed in the early 1990s by SGI and has a long history of running on extremely large servers and storage arrays.
The features of XFS include:
- Reliability
- Metadata journaling, which ensures file system integrity after a system crash by keeping a record of file system operations that can be replayed when the system is restarted and the file system remounted
- Extensive run-time metadata consistency checking
- Scalable and fast repair utilities
- Quota journaling. This avoids the need for lengthy quota consistency checks after a crash.
- Scalability and performance
- Supported file system size up to 1024 TiB
- Ability to support a large number of concurrent operations
- B-tree indexing for scalability of free space management
- Sophisticated metadata read-ahead algorithms
- Optimizations for streaming video workloads
- Allocation schemes
- Extent-based allocation
- Stripe-aware allocation policies
- Delayed allocation
- Space pre-allocation
- Dynamically allocated inodes
- Other features
- Reflink-based file copies
- Tightly integrated backup and restore utilities
- Online defragmentation
- Online file system growing
- Comprehensive diagnostics capabilities
-
Extended attributes (
xattr
). This allows the system to associate several additional name/value pairs per file. - Project or directory quotas. This allows quota restrictions over a directory tree.
- Subsecond timestamps
Performance characteristics
XFS has a high performance on large systems with enterprise workloads. A large system is one with a relatively high number of CPUs, multiple HBAs, and connections to external disk arrays. XFS also performs well on smaller systems that have a multi-threaded, parallel I/O workload.
XFS has a relatively low performance for single threaded, metadata-intensive workloads: for example, a workload that creates or deletes large numbers of small files in a single thread.
1.4. The ext4 file system
The ext4 file system is the fourth generation of the ext file system family. It was the default file system in Red Hat Enterprise Linux 6.
The ext4 driver can read and write to ext2 and ext3 file systems, but the ext4 file system format is not compatible with ext2 and ext3 drivers.
ext4 adds several new and improved features, such as:
- Supported file system size up to 50 TiB
- Extent-based metadata
- Delayed allocation
- Journal checksumming
- Large storage support
The extent-based metadata and the delayed allocation features provide a more compact and efficient way to track utilized space in a file system. These features improve file system performance and reduce the space consumed by metadata. Delayed allocation allows the file system to postpone selection of the permanent location for newly written user data until the data is flushed to disk. This enables higher performance since it can allow for larger, more contiguous allocations, allowing the file system to make decisions with much better information.
File system repair time using the fsck
utility in ext4 is much faster than in ext2 and ext3. Some file system repairs have demonstrated up to a six-fold increase in performance.
1.5. Comparison of XFS and ext4
XFS is the default file system in RHEL. This section compares the usage and features of XFS and ext4.
- Metadata error behavior
-
In ext4, you can configure the behavior when the file system encounters metadata errors. The default behavior is to simply continue the operation. When XFS encounters an unrecoverable metadata error, it shuts down the file system and returns the
EFSCORRUPTED
error. - Quotas
In ext4, you can enable quotas when creating the file system or later on an existing file system. You can then configure the quota enforcement using a mount option.
XFS quotas are not a remountable option. You must activate quotas on the initial mount.
Running the
quotacheck
command on an XFS file system has no effect. The first time you turn on quota accounting, XFS checks quotas automatically.- File system resize
- XFS has no utility to reduce the size of a file system. You can only increase the size of an XFS file system. In comparison, ext4 supports both extending and reducing the size of a file system.
- Inode numbers
The ext4 file system does not support more than 232 inodes.
XFS supports dynamic inode allocation. The amount of space inodes can consume on an XFS filesystem is calculated as a percentage of the total filesystem space. To prevent the system from running out of inodes, an administrator can tune this percentage after the filesystem has been created, given there is free space left on the file system.
Certain applications cannot properly handle inode numbers larger than 232 on an XFS file system. These applications might cause the failure of 32-bit stat calls with the
EOVERFLOW
return value. Inode number exceed 232 under the following conditions:- The file system is larger than 1 TiB with 256-byte inodes.
- The file system is larger than 2 TiB with 512-byte inodes.
If your application fails with large inode numbers, mount the XFS file system with the
-o inode32
option to enforce inode numbers below 232. Note that usinginode32
does not affect inodes that are already allocated with 64-bit numbers.ImportantDo not use the
inode32
option unless a specific environment requires it. Theinode32
option changes allocation behavior. As a consequence, theENOSPC
error might occur if no space is available to allocate inodes in the lower disk blocks.
1.6. Choosing a local file system
To choose a file system that meets your application requirements, you must understand the target system on which you will deploy the file system. In general, use XFS unless you have a specific use case for ext4.
- XFS
- For large-scale deployments, use XFS, particularly when handling large files (hundreds of megabytes) and high I/O concurrency. XFS performs optimally in environments with high bandwidth (greater than 200MB/s) and more than 1000 IOPS. However, it consumes more CPU resources for metadata operations compared to ext4 and does not support file system shrinking.
- ext4
- For smaller systems or environments with limited I/O bandwidth, ext4 might be a better fit. It performs better in single-threaded, lower I/O workloads and environments with lower throughput requirements. ext4 also supports offline shrinking, which can be beneficial if resizing the file system is a requirement.
Benchmark your application’s performance on your target server and storage system to ensure the selected file system meets your performance and scalability requirements.
Scenario | Recommended file system |
---|---|
No special use case | XFS |
Large server | XFS |
Large storage devices | XFS |
Large files | XFS |
Multi-threaded I/O | XFS |
Single-threaded I/O | ext4 |
Limited I/O capability (under 1000 IOPS) | ext4 |
Limited bandwidth (under 200MB/s) | ext4 |
CPU-bound workload | ext4 |
Support for offline shrinking | ext4 |
1.7. Network file systems
Network file systems, also referred to as client/server file systems, enable client systems to access files that are stored on a shared server. This makes it possible for multiple users on multiple systems to share files and storage resources.
Such file systems are built from one or more servers that export a set of file systems to one or more clients. The client nodes do not have access to the underlying block storage, but rather interact with the storage using a protocol that allows for better access control.
- Available network file systems
- The most common client/server file system for RHEL customers is the NFS file system. RHEL provides both an NFS server component to export a local file system over the network and an NFS client to import these file systems.
- RHEL also includes a CIFS client that supports the popular Microsoft SMB file servers for Windows interoperability. The userspace Samba server provides Windows clients with a Microsoft SMB service from a RHEL server.
1.10. Volume-managing file systems
Volume-managing file systems integrate the entire storage stack for the purposes of simplicity and in-stack optimization.
- Available volume-managing file systems
- Red Hat Enterprise Linux 8 provides the Stratis volume manager as a Technology Preview. Stratis uses XFS for the file system layer and integrates it with LVM, Device Mapper, and other components.
Stratis was first released in Red Hat Enterprise Linux 8.0. It is conceived to fill the gap created when Red Hat deprecated Btrfs. Stratis 1.0 is an intuitive, command line-based volume manager that can perform significant storage management operations while hiding the complexity from the user:
- Volume management
- Pool creation
- Thin storage pools
- Snapshots
- Automated read cache
Stratis offers powerful features, but currently lacks certain capabilities of other offerings that it might be compared to, such as Btrfs or ZFS. Most notably, it does not support CRCs with self healing.
Chapter 2. Managing local storage by using the RHEL system role
To manage LVM and local file systems (FS) by using Ansible, you can use the storage
role, which is one of the RHEL system roles available in RHEL 8.
Using the storage
role enables you to automate administration of file systems on disks and logical volumes on multiple machines and across all versions of RHEL starting with RHEL 7.7.
For more information about RHEL system roles and how to apply them, see Introduction to RHEL system roles.
2.1. Introduction to the storage
RHEL system role
The storage
role can manage:
- File systems on disks which have not been partitioned
- Complete LVM volume groups including their logical volumes and file systems
- MD RAID volumes and their file systems
With the storage
role, you can perform the following tasks:
- Create a file system
- Remove a file system
- Mount a file system
- Unmount a file system
- Create LVM volume groups
- Remove LVM volume groups
- Create logical volumes
- Remove logical volumes
- Create RAID volumes
- Remove RAID volumes
- Create LVM volume groups with RAID
- Remove LVM volume groups with RAID
- Create encrypted LVM volume groups
- Create LVM logical volumes with RAID
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.2. Creating an XFS file system on a block device by using the storage
RHEL system role
The example Ansible playbook applies the storage
role to create an XFS file system on a block device using the default parameters.
The storage
role can create a file system only on an unpartitioned, whole disk or a logical volume (LV). It cannot create the file system on a partition.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: xfs
-
The volume name (
barefs
in the example) is currently arbitrary. Thestorage
role identifies the volume by the disk device listed under thedisks:
attribute. -
You can omit the
fs_type: xfs
line because XFS is the default file system in RHEL 8. To create the file system on an LV, provide the LVM setup under the
disks:
attribute, including the enclosing volume group. For details, see Managing logical volumes by using the storage RHEL system role.Do not provide the path to the LV device.
-
The volume name (
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.3. Persistently mounting a file system by using the storage
RHEL system role
The example Ansible applies the storage
role to immediately and persistently mount an XFS file system.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: xfs mount_point: /mnt/data mount_user: somebody mount_group: somegroup mount_mode: 0755
-
This playbook adds the file system to the
/etc/fstab
file, and mounts the file system immediately. -
If the file system on the
/dev/sdb
device or the mount point directory do not exist, the playbook creates them.
-
This playbook adds the file system to the
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.4. Managing logical volumes by using the storage
RHEL system role
The example Ansible playbook applies the storage
role to create an LVM logical volume in a volume group.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:- hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_pools: - name: myvg disks: - sda - sdb - sdc volumes: - name: mylv size: 2G fs_type: ext4 mount_point: /mnt/dat
-
The
myvg
volume group consists of the following disks:/dev/sda
,/dev/sdb
, and/dev/sdc
. -
If the
myvg
volume group already exists, the playbook adds the logical volume to the volume group. -
If the
myvg
volume group does not exist, the playbook creates it. -
The playbook creates an Ext4 file system on the
mylv
logical volume, and persistently mounts the file system at/mnt
.
-
The
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.5. Enabling online block discard by using the storage
RHEL system role
The example Ansible playbook applies the storage
role to mount an XFS file system with online block discard enabled.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: xfs mount_point: /mnt/data mount_options: discard
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.6. Creating and mounting an Ext4 file system by using the storage
RHEL system role
The example Ansible playbook applies the storage
role to create and mount an Ext4 file system.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: ext4 fs_label: label-name mount_point: /mnt/data
-
The playbook creates the file system on the
/dev/sdb
disk. -
The playbook persistently mounts the file system at the
/mnt/data
directory. -
The label of the file system is
label-name
.
-
The playbook creates the file system on the
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.7. Creating and mounting an Ext3 file system by using the storage
RHEL system role
The example Ansible playbook applies the storage
role to create and mount an Ext3 file system.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - hosts: all roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: ext3 fs_label: label-name mount_point: /mnt/data mount_user: somebody mount_group: somegroup mount_mode: 0755
-
The playbook creates the file system on the
/dev/sdb
disk. -
The playbook persistently mounts the file system at the
/mnt/data
directory. -
The label of the file system is
label-name
.
-
The playbook creates the file system on the
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.8. Resizing an existing file system on LVM by using the storage
RHEL system role
The example Ansible playbook applies the storage
RHEL system role to resize an LVM logical volume with a file system.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Create LVM pool over three disks hosts: managed-node-01.example.com tasks: - name: Resize LVM logical volume with file system ansible.builtin.include_role: name: rhel-system-roles.storage vars: storage_pools: - name: myvg disks: - /dev/sda - /dev/sdb - /dev/sdc volumes: - name: mylv1 size: 10 GiB fs_type: ext4 mount_point: /opt/mount1 - name: mylv2 size: 50 GiB fs_type: ext4 mount_point: /opt/mount2
This playbook resizes the following existing file systems:
-
The Ext4 file system on the
mylv1
volume, which is mounted at/opt/mount1
, resizes to 10 GiB. -
The Ext4 file system on the
mylv2
volume, which is mounted at/opt/mount2
, resizes to 50 GiB.
-
The Ext4 file system on the
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.9. Creating a swap volume by using the storage
RHEL system role
This section provides an example Ansible playbook. This playbook applies the storage
role to create a swap volume, if it does not exist, or to modify the swap volume, if it already exist, on a block device by using the default parameters.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Create a disk device with swap hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: swap_fs type: disk disks: - /dev/sdb size: 15 GiB fs_type: swap
The volume name (
swap_fs
in the example) is currently arbitrary. Thestorage
role identifies the volume by the disk device listed under thedisks:
attribute.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.10. Configuring a RAID volume by using the storage
RHEL system role
With the storage
system role, you can configure a RAID volume on RHEL by using Red Hat Ansible Automation Platform and Ansible-Core. Create an Ansible playbook with the parameters to configure a RAID volume to suit your requirements.
Device names might change in certain circumstances, for example, when you add a new disk to a system. Therefore, to prevent data loss, do not use specific disk names in the playbook.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Configure the storage hosts: managed-node-01.example.com tasks: - name: Create a RAID on sdd, sde, sdf, and sdg ansible.builtin.include_role: name: rhel-system-roles.storage vars: storage_safe_mode: false storage_volumes: - name: data type: raid disks: [sdd, sde, sdf, sdg] raid_level: raid0 raid_chunk_size: 32 KiB mount_point: /mnt/data state: present
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory - Managing RAID
2.11. Configuring an LVM pool with RAID by using the storage
RHEL system role
With the storage
system role, you can configure an LVM pool with RAID on RHEL by using Red Hat Ansible Automation Platform. You can set up an Ansible playbook with the available parameters to configure an LVM pool with RAID.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Configure LVM pool with RAID hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_safe_mode: false storage_pools: - name: my_pool type: lvm disks: [sdh, sdi] raid_level: raid1 volumes: - name: my_volume size: "1 GiB" mount_point: "/mnt/app/shared" fs_type: xfs state: present
To create an LVM pool with RAID, you must specify the RAID type by using the
raid_level
parameter.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory - Managing RAID
2.12. Configuring a stripe size for RAID LVM volumes by using the storage
RHEL system role
With the storage
system role, you can configure a stripe size for RAID LVM volumes on RHEL by using Red Hat Ansible Automation Platform. You can set up an Ansible playbook with the available parameters to configure an LVM pool with RAID.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Configure stripe size for RAID LVM volumes hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_safe_mode: false storage_pools: - name: my_pool type: lvm disks: [sdh, sdi] volumes: - name: my_volume size: "1 GiB" mount_point: "/mnt/app/shared" fs_type: xfs raid_level: raid1 raid_stripe_size: "256 KiB" state: present
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory - Managing RAID
2.13. Compressing and deduplicating a VDO volume on LVM by using the storage
RHEL system role
The example Ansible playbook applies the storage
RHEL system role to enable compression and deduplication of Logical Volumes (LVM) by using Virtual Data Optimizer (VDO).
Because of the storage
system role use of LVM VDO, only one volume per pool can use the compression and deduplication.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:- name: Create LVM VDO volume under volume group 'myvg' hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_pools: - name: myvg disks: - /dev/sdb volumes: - name: mylv1 compression: true deduplication: true vdo_pool_size: 10 GiB size: 30 GiB mount_point: /mnt/app/shared
In this example, the
compression
anddeduplication
pools are set to true, which specifies that the VDO is used. The following describes the usage of these parameters:-
The
deduplication
is used to deduplicate the duplicated data stored on the storage volume. - The compression is used to compress the data stored on the storage volume, which results in more storage capacity.
-
The vdo_pool_size specifies the actual size the volume takes on the device. The virtual size of VDO volume is set by the
size
parameter.
-
The
Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
2.14. Creating a LUKS2 encrypted volume by using the storage
RHEL system role
You can use the storage
role to create and configure a volume encrypted with LUKS by running an Ansible playbook.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Create and configure a volume encrypted with LUKS hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: xfs fs_label: label-name mount_point: /mnt/data encryption: true encryption_password: <password>
You can also add other encryption parameters, such as
encryption_key
,encryption_cipher
,encryption_key_size
, andencryption_luks
, to the playbook file.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Verification
View the encryption status:
# cryptsetup status sdb /dev/mapper/sdb is active and is in use. type: LUKS2 cipher: aes-xts-plain64 keysize: 512 bits key location: keyring device: /dev/sdb ...
Verify the created LUKS encrypted volume:
# cryptsetup luksDump /dev/sdb Version: 2 Epoch: 6 Metadata area: 16384 [bytes] Keyslots area: 33521664 [bytes] UUID: a4c6be82-7347-4a91-a8ad-9479b72c9426 Label: (no label) Subsystem: (no subsystem) Flags: allow-discards Data segments: 0: crypt offset: 33554432 [bytes] length: (whole device) cipher: aes-xts-plain64 sector: 4096 [bytes] ...
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory - Encrypting block devices by using LUKS
2.15. Expressing pool volume sizes as percentage by using the storage
RHEL system role
The example Ansible playbook applies the storage
system role to enable you to express Logical Manager Volumes (LVM) volume sizes as a percentage of the pool’s total size.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Express volume sizes as a percentage of the pool's total size hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_pools: - name: myvg disks: - /dev/sdb volumes: - name: data size: 60% mount_point: /opt/mount/data - name: web size: 30% mount_point: /opt/mount/web - name: cache size: 10% mount_point: /opt/cache/mount
This example specifies the size of LVM volumes as a percentage of the pool size, for example:
60%
. Alternatively, you can also specify the size of LVM volumes as a percentage of the pool size in a human-readable size of the file system, for example,10g
or50 GiB
.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory
Chapter 3. Managing partitions using the web console
Learn how to manage file systems on RHEL 8 using the web console.
3.1. Displaying partitions formatted with file systems in the web console
The Storage section in the web console displays all available file systems in the Filesystems table.
Besides the list of partitions formatted with file systems, you can also use the page for creating new storage.
Prerequisites
-
The
cockpit-storaged
package is installed on your system.
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
Click the Storage tab.
In the Storage table, you can see all available partitions formatted with file systems, their ID, types, locations, sizes, and how much space is available on each partition.
You can also use the drop-down menu in the top-right corner to create new local or networked storage.
3.2. Creating partitions in the web console
To create a new partition:
- Use an existing partition table
- Create a partition
Prerequisites
-
The
cockpit-storaged
package is installed on your system. - The web console must be installed and accessible. For details, see Installing the web console.
- An unformatted volume connected to the system is visible in the Storage table of the Storage tab.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click the Storage tab.
- In the Storage table, click the device which you want to partition to open the page and options for that device.
- On the device page, click the menu button, Create partition table. , and select
In the Initialize disk dialog box, select the following:
Partitioning:
- Compatible with all systems and devices (MBR)
- Compatible with modern system and hard disks > 2TB (GPT)
- No partitioning
Overwrite:
Select the Overwrite existing data with zeros checkbox if you want the RHEL web console to rewrite the whole disk with zeros. This option is slower because the program has to go through the whole disk, but it is more secure. Use this option if the disk includes any data and you need to overwrite it.
If you do not select the Overwrite existing data with zeros checkbox, the RHEL web console rewrites only the disk header. This increases the speed of formatting.
- Click .
- Click the menu button, Free space by default. , next to the partition table you created. It is named
- Click .
- In the Create partition dialog box, enter a Name for the file system.
- Add a Mount point.
In the Type drop-down menu, select a file system:
- XFS file system supports large logical volumes, switching physical drives online without outage, and growing an existing file system. Leave this file system selected if you do not have a different strong preference.
ext4 file system supports:
- Logical volumes
- Switching physical drives online without outage
- Growing a file system
- Shrinking a file system
Additional option is to enable encryption of partition done by LUKS (Linux Unified Key Setup), which allows you to encrypt the volume with a passphrase.
- Enter the Size of the volume you want to create.
Select the Overwrite existing data with zeros checkbox if you want the RHEL web console to rewrite the whole disk with zeros. This option is slower because the program has to go through the whole disk, but it is more secure. Use this option if the disk includes any data and you need to overwrite it.
If you do not select the Overwrite existing data with zeros checkbox, the RHEL web console rewrites only the disk header. This increases the speed of formatting.
If you want to encrypt the volume, select the type of encryption in the Encryption drop-down menu.
If you do not want to encrypt the volume, select No encryption.
- In the At boot drop-down menu, select when you want to mount the volume.
In Mount options section:
- Select the Mount read only checkbox if you want the to mount the volume as a read-only logical volume.
- Select the Custom mount options checkbox and add the mount options if you want to change the default mount option.
Create the partition:
- If you want to create and mount the partition, click the button.
If you want to only create the partition, click the
button.Formatting can take several minutes depending on the volume size and which formatting options are selected.
Verification
- To verify that the partition has been successfully added, switch to the Storage tab and check the Storage table and verify whether the new partition is listed.
3.3. Deleting partitions in the web console
You can remove partitions in the web console interface.
Prerequisites
-
The
cockpit-storaged
package is installed on your system.
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click the Storage tab.
- Click the device from which you want to delete a partition.
- On the device page and in the GPT partitions section, click the menu button, next to the partition you want to delete.
From the drop-down menu, select
.The RHEL web console terminates all processes that are currently using the partition and unmount the partition before deleting it.
Verification
- To verify that the partition has been successfully removed, switch to the Storage tab and check the Storage table.
Chapter 6. Overview of persistent naming attributes
As a system administrator, you need to refer to storage volumes using persistent naming attributes to build storage setups that are reliable over multiple system boots.
6.1. Disadvantages of non-persistent naming attributes
Red Hat Enterprise Linux provides a number of ways to identify storage devices. It is important to use the correct option to identify each device when used in order to avoid inadvertently accessing the wrong device, particularly when installing to or reformatting drives.
Traditionally, non-persistent names in the form of /dev/sd(major number)(minor number)
are used on Linux to refer to storage devices. The major and minor number range and associated sd
names are allocated for each device when it is detected. This means that the association between the major and minor number range and associated sd
names can change if the order of device detection changes.
Such a change in the ordering might occur in the following situations:
- The parallelization of the system boot process detects storage devices in a different order with each system boot.
-
A disk fails to power up or respond to the SCSI controller. This results in it not being detected by the normal device probe. The disk is not accessible to the system and subsequent devices will have their major and minor number range, including the associated
sd
names shifted down. For example, if a disk normally referred to assdb
is not detected, a disk that is normally referred to assdc
would instead appear assdb
. -
A SCSI controller (host bus adapter, or HBA) fails to initialize, causing all disks connected to that HBA to not be detected. Any disks connected to subsequently probed HBAs are assigned different major and minor number ranges, and different associated
sd
names. - The order of driver initialization changes if different types of HBAs are present in the system. This causes the disks connected to those HBAs to be detected in a different order. This might also occur if HBAs are moved to different PCI slots on the system.
-
Disks connected to the system with Fibre Channel, iSCSI, or FCoE adapters might be inaccessible at the time the storage devices are probed, due to a storage array or intervening switch being powered off, for example. This might occur when a system reboots after a power failure, if the storage array takes longer to come online than the system take to boot. Although some Fibre Channel drivers support a mechanism to specify a persistent SCSI target ID to WWPN mapping, this does not cause the major and minor number ranges, and the associated
sd
names to be reserved; it only provides consistent SCSI target ID numbers.
These reasons make it undesirable to use the major and minor number range or the associated sd
names when referring to devices, such as in the /etc/fstab
file. There is the possibility that the wrong device will be mounted and data corruption might result.
Occasionally, however, it is still necessary to refer to the sd
names even when another mechanism is used, such as when errors are reported by a device. This is because the Linux kernel uses sd
names (and also SCSI host/channel/target/LUN tuples) in kernel messages regarding the device.
6.2. File system and device identifiers
File system identifiers are tied to the file system itself, while device identifiers are linked to the physical block device. Understanding the difference is important for proper storage management.
File system identifiers
File system identifiers are tied to a particular file system created on a block device. The identifier is also stored as part of the file system. If you copy the file system to a different device, it still carries the same file system identifier. However, if you rewrite the device, such as by formatting it with the mkfs
utility, the device loses the attribute.
File system identifiers include:
- Unique identifier (UUID)
- Label
Device identifiers
Device identifiers are tied to a block device: for example, a disk or a partition. If you rewrite the device, such as by formatting it with the mkfs
utility, the device keeps the attribute, because it is not stored in the file system.
Device identifiers include:
- World Wide Identifier (WWID)
- Partition UUID
- Serial number
Recommendations
- Some file systems, such as logical volumes, span multiple devices. Red Hat recommends accessing these file systems using file system identifiers rather than device identifiers.
6.3. Device names managed by the udev mechanism in /dev/disk/
The udev
mechanism is used for all types of devices in Linux, and is not limited only for storage devices. It provides different kinds of persistent naming attributes in the /dev/disk/
directory. In the case of storage devices, Red Hat Enterprise Linux contains udev
rules that create symbolic links in the /dev/disk/
directory. This enables you to refer to storage devices by:
- Their content
- A unique identifier
- Their serial number.
Although udev
naming attributes are persistent, in that they do not change on their own across system reboots, some are also configurable.
6.3.1. File system identifiers
The UUID attribute in /dev/disk/by-uuid/
Entries in this directory provide a symbolic name that refers to the storage device by a unique identifier (UUID) in the content (that is, the data) stored on the device. For example:
/dev/disk/by-uuid/3e6be9de-8139-11d1-9106-a43f08d823a6
You can use the UUID to refer to the device in the /etc/fstab
file using the following syntax:
UUID=3e6be9de-8139-11d1-9106-a43f08d823a6
You can configure the UUID attribute when creating a file system, and you can also change it later on.
The Label attribute in /dev/disk/by-label/
Entries in this directory provide a symbolic name that refers to the storage device by a label in the content (that is, the data) stored on the device.
For example:
/dev/disk/by-label/Boot
You can use the label to refer to the device in the /etc/fstab
file using the following syntax:
LABEL=Boot
You can configure the Label attribute when creating a file system, and you can also change it later on.
6.3.2. Device identifiers
The WWID attribute in /dev/disk/by-id/
The World Wide Identifier (WWID) is a persistent, system-independent identifier that the SCSI Standard requires from all SCSI devices. The WWID identifier is guaranteed to be unique for every storage device, and independent of the path that is used to access the device. The identifier is a property of the device but is not stored in the content (that is, the data) on the devices.
This identifier can be obtained by issuing a SCSI Inquiry to retrieve the Device Identification Vital Product Data (page 0x83
) or Unit Serial Number (page 0x80
).
Red Hat Enterprise Linux automatically maintains the proper mapping from the WWID-based device name to a current /dev/sd
name on that system. Applications can use the /dev/disk/by-id/
name to reference the data on the disk, even if the path to the device changes, and even when accessing the device from different systems.
Example 6.1. WWID mappings
WWID symlink | Non-persistent device | Note |
---|---|---|
|
|
A device with a page |
|
|
A device with a page |
|
| A disk partition |
In addition to these persistent names provided by the system, you can also use udev
rules to implement persistent names of your own, mapped to the WWID of the storage.
The Partition UUID attribute in /dev/disk/by-partuuid
The Partition UUID (PARTUUID) attribute identifies partitions as defined by GPT partition table.
Example 6.2. Partition UUID mappings
PARTUUID symlink | Non-persistent device |
---|---|
|
|
|
|
|
|
The Path attribute in /dev/disk/by-path/
This attribute provides a symbolic name that refers to the storage device by the hardware path used to access the device.
The Path attribute fails if any part of the hardware path (for example, the PCI ID, target port, or LUN number) changes. The Path attribute is therefore unreliable. However, the Path attribute may be useful in one of the following scenarios:
- You need to identify a disk that you are planning to replace later.
- You plan to install a storage service on a disk in a specific location.
6.4. The World Wide Identifier with DM Multipath
You can configure Device Mapper (DM) Multipath to map between the World Wide Identifier (WWID) and non-persistent device names.
If there are multiple paths from a system to a device, DM Multipath uses the WWID to detect this. DM Multipath then presents a single "pseudo-device" in the /dev/mapper/wwid
directory, such as /dev/mapper/3600508b400105df70000e00000ac0000
.
The command multipath -l
shows the mapping to the non-persistent identifiers:
-
Host:Channel:Target:LUN
-
/dev/sd
name -
major:minor
number
Example 6.3. WWID mappings in a multipath configuration
An example output of the multipath -l
command:
3600508b400105df70000e00000ac0000 dm-2 vendor,product [size=20G][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=0][active] \_ 5:0:1:1 sdc 8:32 [active][undef] \_ 6:0:1:1 sdg 8:96 [active][undef] \_ round-robin 0 [prio=0][enabled] \_ 5:0:0:1 sdb 8:16 [active][undef] \_ 6:0:0:1 sdf 8:80 [active][undef]
DM Multipath automatically maintains the proper mapping of each WWID-based device name to its corresponding /dev/sd
name on the system. These names are persistent across path changes, and they are consistent when accessing the device from different systems.
When the user_friendly_names
feature of DM Multipath is used, the WWID is mapped to a name of the form /dev/mapper/mpathN
. By default, this mapping is maintained in the file /etc/multipath/bindings
. These mpathN
names are persistent as long as that file is maintained.
If you use user_friendly_names
, then additional steps are required to obtain consistent names in a cluster.
6.5. Limitations of the udev device naming convention
The following are some limitations of the udev
naming convention:
-
It is possible that the device might not be accessible at the time the query is performed because the
udev
mechanism might rely on the ability to query the storage device when theudev
rules are processed for audev
event. This is more likely to occur with Fibre Channel, iSCSI or FCoE storage devices when the device is not located in the server chassis. -
The kernel might send
udev
events at any time, causing the rules to be processed and possibly causing the/dev/disk/by-*/
links to be removed if the device is not accessible. -
There might be a delay between when the
udev
event is generated and when it is processed, such as when a large number of devices are detected and the user-spaceudevd
service takes some amount of time to process the rules for each one. This might cause a delay between when the kernel detects the device and when the/dev/disk/by-*/
names are available. -
External programs such as
blkid
invoked by the rules might open the device for a brief period of time, making the device inaccessible for other uses. -
The device names managed by the
udev
mechanism in /dev/disk/ may change between major releases, requiring you to update the links.
6.6. Listing persistent naming attributes
You can find out the persistent naming attributes of non-persistent storage devices.
Procedure
To list the UUID and Label attributes, use the
lsblk
utility:$ lsblk --fs storage-device
For example:
Example 6.4. Viewing the UUID and Label of a file system
$ lsblk --fs /dev/sda1 NAME FSTYPE LABEL UUID MOUNTPOINT sda1 xfs Boot afa5d5e3-9050-48c3-acc1-bb30095f3dc4 /boot
To list the PARTUUID attribute, use the
lsblk
utility with the--output +PARTUUID
option:$ lsblk --output +PARTUUID
For example:
Example 6.5. Viewing the PARTUUID attribute of a partition
$ lsblk --output +PARTUUID /dev/sda1 NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT PARTUUID sda1 8:1 0 512M 0 part /boot 4cd1448a-01
To list the WWID attribute, examine the targets of symbolic links in the
/dev/disk/by-id/
directory. For example:Example 6.6. Viewing the WWID of all storage devices on the system
$ file /dev/disk/by-id/* /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001 symbolic link to ../../sda /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part1 symbolic link to ../../sda1 /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part2 symbolic link to ../../sda2 /dev/disk/by-id/dm-name-rhel_rhel8-root symbolic link to ../../dm-0 /dev/disk/by-id/dm-name-rhel_rhel8-swap symbolic link to ../../dm-1 /dev/disk/by-id/dm-uuid-LVM-QIWtEHtXGobe5bewlIUDivKOz5ofkgFhP0RMFsNyySVihqEl2cWWbR7MjXJolD6g symbolic link to ../../dm-1 /dev/disk/by-id/dm-uuid-LVM-QIWtEHtXGobe5bewlIUDivKOz5ofkgFhXqH2M45hD2H9nAf2qfWSrlRLhzfMyOKd symbolic link to ../../dm-0 /dev/disk/by-id/lvm-pv-uuid-atlr2Y-vuMo-ueoH-CpMG-4JuH-AhEF-wu4QQm symbolic link to ../../sda2
6.7. Modifying persistent naming attributes
You can change the UUID or Label persistent naming attribute of a file system.
Changing udev
attributes happens in the background and might take a long time. The udevadm settle
command waits until the change is fully registered, which ensures that your next command will be able to use the new attribute correctly.
In the following commands:
-
Replace new-uuid with the UUID you want to set; for example,
1cdfbc07-1c90-4984-b5ec-f61943f5ea50
. You can generate a UUID using theuuidgen
command. -
Replace new-label with a label; for example,
backup_data
.
Prerequisites
- If you are modifying the attributes of an XFS file system, unmount it first.
Procedure
To change the UUID or Label attributes of an XFS file system, use the
xfs_admin
utility:# xfs_admin -U new-uuid -L new-label storage-device # udevadm settle
To change the UUID or Label attributes of an ext4, ext3, or ext2 file system, use the
tune2fs
utility:# tune2fs -U new-uuid -L new-label storage-device # udevadm settle
To change the UUID or Label attributes of a swap volume, use the
swaplabel
utility:# swaplabel --uuid new-uuid --label new-label swap-device # udevadm settle
Chapter 7. Partition operations with parted
parted
is a program to manipulate disk partitions. It supports multiple partition table formats, including MS-DOS and GPT. It is useful for creating space for new operating systems, reorganizing disk usage, and copying data to new hard disks.
7.1. Viewing the partition table with parted
Display the partition table of a block device to see the partition layout and details about individual partitions. You can view the partition table on a block device using the parted
utility.
Procedure
Start the
parted
utility. For example, the following output lists the device/dev/sda
:# parted /dev/sda
View the partition table:
# (parted) print Model: ATA SAMSUNG MZNLN256 (scsi) Disk /dev/sda: 256GB Sector size (logical/physical): 512B/512B Partition Table: msdos Disk Flags: Number Start End Size Type File system Flags 1 1049kB 269MB 268MB primary xfs boot 2 269MB 34.6GB 34.4GB primary 3 34.6GB 45.4GB 10.7GB primary 4 45.4GB 256GB 211GB extended 5 45.4GB 256GB 211GB logical
Optional: Switch to the device you want to examine next:
# (parted) select block-device
For a detailed description of the print command output, see the following:
Model: ATA SAMSUNG MZNLN256 (scsi)
- The disk type, manufacturer, model number, and interface.
Disk /dev/sda: 256GB
- The file path to the block device and the storage capacity.
Partition Table: msdos
- The disk label type.
Number
-
The partition number. For example, the partition with minor number 1 corresponds to
/dev/sda1
. Start
andEnd
- The location on the device where the partition starts and ends.
Type
- Valid types are metadata, free, primary, extended, or logical.
File system
-
The file system type. If the
File system
field of a device shows no value, this means that its file system type is unknown. Theparted
utility cannot recognize the file system on encrypted devices. Flags
-
Lists the flags set for the partition. Available flags are
boot
,root
,swap
,hidden
,raid
,lvm
, orlba
.
Additional resources
-
parted(8)
man page on your system
7.2. Creating a partition table on a disk with parted
Use the parted
utility to format a block device with a partition table more easily.
Formatting a block device with a partition table deletes all data stored on the device.
Procedure
Start the interactive
parted
shell:# parted block-device
Determine if there already is a partition table on the device:
# (parted) print
If the device already contains partitions, they will be deleted in the following steps.
Create the new partition table:
# (parted) mklabel table-type
Replace table-type with with the intended partition table type:
-
msdos
for MBR -
gpt
for GPT
-
Example 7.1. Creating a GUID Partition Table (GPT) table
To create a GPT table on the disk, use:
# (parted) mklabel gpt
The changes start applying after you enter this command.
View the partition table to confirm that it is created:
# (parted) print
Exit the
parted
shell:# (parted) quit
Additional resources
-
parted(8)
man page on your system
7.3. Creating a partition with parted
As a system administrator, you can create new partitions on a disk by using the parted
utility.
The required partitions are swap
, /boot/
, and / (root)
.
Prerequisites
- A partition table on the disk.
- If the partition you want to create is larger than 2TiB, format the disk with the GUID Partition Table (GPT).
Procedure
Start the
parted
utility:# parted block-device
View the current partition table to determine if there is enough free space:
# (parted) print
- Resize the partition in case there is not enough free space.
From the partition table, determine:
- The start and end points of the new partition.
- On MBR, what partition type it should be.
Create the new partition:
# (parted) mkpart part-type name fs-type start end
-
Replace part-type with with
primary
,logical
, orextended
. This applies only to the MBR partition table. - Replace name with an arbitrary partition name. This is required for GPT partition tables.
-
Replace fs-type with
xfs
,ext2
,ext3
,ext4
,fat16
,fat32
,hfs
,hfs+
,linux-swap
,ntfs
, orreiserfs
. The fs-type parameter is optional. Note that theparted
utility does not create the file system on the partition. -
Replace start and end with the sizes that determine the starting and ending points of the partition, counting from the beginning of the disk. You can use size suffixes, such as
512MiB
,20GiB
, or1.5TiB
. The default size is in megabytes.
Example 7.2. Creating a small primary partition
To create a primary partition from 1024MiB until 2048MiB on an MBR table, use:
# (parted) mkpart primary 1024MiB 2048MiB
The changes start applying after you enter the command.
-
Replace part-type with with
View the partition table to confirm that the created partition is in the partition table with the correct partition type, file system type, and size:
# (parted) print
Exit the
parted
shell:# (parted) quit
Register the new device node:
# udevadm settle
Verify that the kernel recognizes the new partition:
# cat /proc/partitions
Additional resources
-
parted(8)
man page on your system - Creating a partition table on a disk with parted.
- Resizing a partition with parted
7.4. Removing a partition with parted
Using the parted
utility, you can remove a disk partition to free up disk space.
Removing a partition deletes all data stored on the partition.
Procedure
Start the interactive
parted
shell:# parted block-device
-
Replace block-device with the path to the device where you want to remove a partition: for example,
/dev/sda
.
-
Replace block-device with the path to the device where you want to remove a partition: for example,
View the current partition table to determine the minor number of the partition to remove:
(parted) print
Remove the partition:
(parted) rm minor-number
- Replace minor-number with the minor number of the partition you want to remove.
The changes start applying as soon as you enter this command.
Verify that you have removed the partition from the partition table:
(parted) print
Exit the
parted
shell:(parted) quit
Verify that the kernel registers that the partition is removed:
# cat /proc/partitions
-
Remove the partition from the
/etc/fstab
file, if it is present. Find the line that declares the removed partition, and remove it from the file. Regenerate mount units so that your system registers the new
/etc/fstab
configuration:# systemctl daemon-reload
If you have deleted a swap partition or removed pieces of LVM, remove all references to the partition from the kernel command line:
List active kernel options and see if any option references the removed partition:
# grubby --info=ALL
Remove the kernel options that reference the removed partition:
# grubby --update-kernel=ALL --remove-args="option"
To register the changes in the early boot system, rebuild the
initramfs
file system:# dracut --force --verbose
Additional resources
-
parted(8)
man page on your system
7.5. Resizing a partition with parted
Using the parted
utility, extend a partition to use unused disk space, or shrink a partition to use its capacity for different purposes.
Prerequisites
- Back up the data before shrinking a partition.
- If the partition you want to create is larger than 2TiB, format the disk with the GUID Partition Table (GPT).
- If you want to shrink the partition, first shrink the file system so that it is not larger than the resized partition.
XFS does not support shrinking.
Procedure
Start the
parted
utility:# parted block-device
View the current partition table:
# (parted) print
From the partition table, determine:
- The minor number of the partition.
- The location of the existing partition and its new ending point after resizing.
Resize the partition:
# (parted) resizepart 1 2GiB
- Replace 1 with the minor number of the partition that you are resizing.
-
Replace 2 with the size that determines the new ending point of the resized partition, counting from the beginning of the disk. You can use size suffixes, such as
512MiB
,20GiB
, or1.5TiB
. The default size is in megabytes.
View the partition table to confirm that the resized partition is in the partition table with the correct size:
# (parted) print
Exit the
parted
shell:# (parted) quit
Verify that the kernel registers the new partition:
# cat /proc/partitions
- Optional: If you extended the partition, extend the file system on it as well.
Additional resources
-
parted(8)
man page.
Chapter 8. Strategies for repartitioning a disk
There are different approaches to repartitioning a disk. These include:
- Unpartitioned free space is available.
- An unused partition is available.
- Free space in an actively used partition is available.
The following examples are simplified for clarity and do not reflect the exact partition layout when actually installing Red Hat Enterprise Linux.
8.1. Using unpartitioned free space
Partitions that are already defined and do not span the entire hard disk, leave unallocated space that is not part of any defined partition. The following diagram shows what this might look like.
Figure 8.1. Disk with unpartitioned free space
The first diagram represents a disk with one primary partition and an undefined partition with unallocated space. The second diagram represents a disk with two defined partitions with allocated space.
An unused hard disk also falls into this category. The only difference is that all the space is not part of any defined partition.
On a new disk, you can create the necessary partitions from the unused space. Most preinstalled operating systems are configured to take up all available space on a disk drive.
8.2. Using space from an unused partition
In the following example, the first diagram represents a disk with an unused partition. The second diagram represents reallocating an unused partition for Linux.
Figure 8.2. Disk with an unused partition
To use the space allocated to the unused partition, delete the partition and then create the appropriate Linux partition instead. Alternatively, during the installation process, delete the unused partition and manually create new partitions.
8.3. Using free space from an active partition
This process can be difficult to manage because an active partition, that is already in use, contains the required free space. In most cases, hard disks of computers with preinstalled software contain one larger partition holding the operating system and data.
If you want to use an operating system (OS) on an active partition, you must reinstall the OS. Be aware that some computers, which include pre-installed software, do not include installation media to reinstall the original OS. Check whether this applies to your OS before you destroy an original partition and the OS installation.
To optimise the use of available free space, you can use the methods of destructive or non-destructive repartitioning.
8.3.1. Destructive repartitioning
Destructive repartitioning destroys the partition on your hard drive and creates several smaller partitions instead. Backup any needed data from the original partition as this method deletes the complete contents.
After creating a smaller partition for your existing operating system, you can:
- Reinstall software.
- Restore your data.
- Start your Red Hat Enterprise Linux installation.
The following diagram is a simplified representation of using the destructive repartitioning method.
Figure 8.3. Destructive repartitioning action on disk
This method deletes all data previously stored in the original partition.
8.3.2. Non-destructive repartitioning
Non-destructive repartitioning resizes partitions, without any data loss. This method is reliable, however it takes longer processing time on large drives.
The following is a list of methods, which can help initiate non-destructive repartitioning.
- Compress existing data
The storage location of some data cannot be changed. This can prevent the resizing of a partition to the required size, and ultimately lead to a destructive repartition process. Compressing data in an already existing partition can help you resize your partitions as needed. It can also help to maximize the free space available.
The following diagram is a simplified representation of this process.
Figure 8.4. Data compression on a disk
To avoid any possible data loss, create a backup before continuing with the compression process.
- Resize the existing partition
By resizing an already existing partition, you can free up more space. Depending on your resizing software, the results may vary. In the majority of cases, you can create a new unformatted partition of the same type, as the original partition.
The steps you take after resizing can depend on the software you use. In the following example, the best practice is to delete the new DOS (Disk Operating System) partition, and create a Linux partition instead. Verify what is most suitable for your disk before initiating the resizing process.
Figure 8.5. Partition resizing on a disk
- Optional: Create new partitions
Some pieces of resizing software support Linux based systems. In such cases, there is no need to delete the newly created partition after resizing. Creating a new partition afterwards depends on the software you use.
The following diagram represents the disk state, before and after creating a new partition.
Figure 8.6. Disk with final partition configuration
Chapter 9. Getting started with XFS
This is an overview of how to create and maintain XFS file systems.
9.1. The XFS file system
XFS is a highly scalable, high-performance, robust, and mature 64-bit journaling file system that supports very large files and file systems on a single host. It is the default file system in Red Hat Enterprise Linux 8. XFS was originally developed in the early 1990s by SGI and has a long history of running on extremely large servers and storage arrays.
The features of XFS include:
- Reliability
- Metadata journaling, which ensures file system integrity after a system crash by keeping a record of file system operations that can be replayed when the system is restarted and the file system remounted
- Extensive run-time metadata consistency checking
- Scalable and fast repair utilities
- Quota journaling. This avoids the need for lengthy quota consistency checks after a crash.
- Scalability and performance
- Supported file system size up to 1024 TiB
- Ability to support a large number of concurrent operations
- B-tree indexing for scalability of free space management
- Sophisticated metadata read-ahead algorithms
- Optimizations for streaming video workloads
- Allocation schemes
- Extent-based allocation
- Stripe-aware allocation policies
- Delayed allocation
- Space pre-allocation
- Dynamically allocated inodes
- Other features
- Reflink-based file copies
- Tightly integrated backup and restore utilities
- Online defragmentation
- Online file system growing
- Comprehensive diagnostics capabilities
-
Extended attributes (
xattr
). This allows the system to associate several additional name/value pairs per file. - Project or directory quotas. This allows quota restrictions over a directory tree.
- Subsecond timestamps
Performance characteristics
XFS has a high performance on large systems with enterprise workloads. A large system is one with a relatively high number of CPUs, multiple HBAs, and connections to external disk arrays. XFS also performs well on smaller systems that have a multi-threaded, parallel I/O workload.
XFS has a relatively low performance for single threaded, metadata-intensive workloads: for example, a workload that creates or deletes large numbers of small files in a single thread.
9.2. Comparison of tools used with ext4 and XFS
This section compares which tools to use to accomplish common tasks on the ext4 and XFS file systems.
Task | ext4 | XFS |
---|---|---|
Create a file system |
|
|
File system check |
|
|
Resize a file system |
|
|
Save an image of a file system |
|
|
Label or tune a file system |
|
|
Back up a file system |
|
|
Quota management |
|
|
File mapping |
|
|
Chapter 10. Creating an XFS file system
As a system administrator, you can create an XFS file system on a block device to enable it to store files and directories.
10.1. Creating an XFS file system with mkfs.xfs
This procedure describes how to create an XFS file system on a block device.
Procedure
To create the file system:
If the device is a regular partition, an LVM volume, an MD volume, a disk, or a similar device, use the following command:
# mkfs.xfs block-device
-
Replace block-device with the path to the block device. For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
. - In general, the default options are optimal for common use.
-
When using
mkfs.xfs
on a block device containing an existing file system, add the-f
option to overwrite that file system.
-
Replace block-device with the path to the block device. For example,
To create the file system on a hardware RAID device, check if the system correctly detects the stripe geometry of the device:
If the stripe geometry information is correct, no additional options are needed. Create the file system:
# mkfs.xfs block-device
If the information is incorrect, specify stripe geometry manually with the
su
andsw
parameters of the-d
option. Thesu
parameter specifies the RAID chunk size, and thesw
parameter specifies the number of data disks in the RAID device.For example:
# mkfs.xfs -d su=64k,sw=4 /dev/sda3
Use the following command to wait for the system to register the new device node:
# udevadm settle
Additional resources
-
mkfs.xfs(8)
man page on your system
Chapter 11. Backing up an XFS file system
As a system administrator, you can use the xfsdump
to back up an XFS file system into a file or on a tape. This provides a simple backup mechanism.
11.1. Features of XFS backup
This section describes key concepts and features of backing up an XFS file system with the xfsdump
utility.
You can use the xfsdump
utility to:
Perform backups to regular file images.
Only one backup can be written to a regular file.
Perform backups to tape drives.
The
xfsdump
utility also enables you to write multiple backups to the same tape. A backup can span multiple tapes.To back up multiple file systems to a single tape device, simply write the backup to a tape that already contains an XFS backup. This appends the new backup to the previous one. By default,
xfsdump
never overwrites existing backups.Create incremental backups.
The
xfsdump
utility uses dump levels to determine a base backup to which other backups are relative. Numbers from 0 to 9 refer to increasing dump levels. An incremental backup only backs up files that have changed since the last dump of a lower level:- To perform a full backup, perform a level 0 dump on the file system.
- A level 1 dump is the first incremental backup after a full backup. The next incremental backup would be level 2, which only backs up files that have changed since the last level 1 dump; and so on, to a maximum of level 9.
- Exclude files from a backup using size, subtree, or inode flags to filter them.
Additional resources
-
xfsdump(8)
man page on your system
11.2. Backing up an XFS file system with xfsdump
This procedure describes how to back up the content of an XFS file system into a file or a tape.
Prerequisites
- An XFS file system that you can back up.
- Another file system or a tape drive where you can store the backup.
Procedure
Use the following command to back up an XFS file system:
# xfsdump -l level [-L label] \ -f backup-destination path-to-xfs-filesystem
-
Replace level with the dump level of your backup. Use
0
to perform a full backup or1
to9
to perform consequent incremental backups. -
Replace backup-destination with the path where you want to store your backup. The destination can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdump
for a file or/dev/st0
for a tape drive. -
Replace path-to-xfs-filesystem with the mount point of the XFS file system you want to back up. For example,
/mnt/data/
. The file system must be mounted. -
When backing up multiple file systems and saving them on a single tape device, add a session label to each backup using the
-L label
option so that it is easier to identify them when restoring. Replace label with any name for your backup: for example,backup_data
.
-
Replace level with the dump level of your backup. Use
Example 11.1. Backing up multiple XFS file systems
To back up the content of XFS file systems mounted on the
/boot/
and/data/
directories and save them as files in the/backup-files/
directory:# xfsdump -l 0 -f /backup-files/boot.xfsdump /boot # xfsdump -l 0 -f /backup-files/data.xfsdump /data
To back up multiple file systems on a single tape device, add a session label to each backup using the
-L label
option:# xfsdump -l 0 -L "backup_boot" -f /dev/st0 /boot # xfsdump -l 0 -L "backup_data" -f /dev/st0 /data
Additional resources
-
xfsdump(8)
man page on your system
Chapter 12. Restoring an XFS file system from backup
As a system administrator, you can use the xfsrestore
utility to restore XFS backup created with the xfsdump
utility and stored in a file or on a tape.
12.1. Features of restoring XFS from backup
The xfsrestore
utility restores file systems from backups produced by xfsdump
. The xfsrestore
utility has two modes:
- The simple mode enables users to restore an entire file system from a level 0 dump. This is the default mode.
- The cumulative mode enables file system restoration from an incremental backup: that is, level 1 to level 9.
A unique session ID or session label identifies each backup. Restoring a backup from a tape containing multiple backups requires its corresponding session ID or label.
To extract, add, or delete specific files from a backup, enter the xfsrestore
interactive mode. The interactive mode provides a set of commands to manipulate the backup files.
Additional resources
-
xfsrestore(8)
man page on your system
12.2. Restoring an XFS file system from backup with xfsrestore
This procedure describes how to restore the content of an XFS file system from a file or tape backup.
Prerequisites
- A file or tape backup of XFS file systems, as described in Backing up an XFS file system.
- A storage device where you can restore the backup.
Procedure
The command to restore the backup varies depending on whether you are restoring from a full backup or an incremental one, or are restoring multiple backups from a single tape device:
# xfsrestore [-r] [-S session-id] [-L session-label] [-i] -f backup-location restoration-path
-
Replace backup-location with the location of the backup. This can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdump
for a file or/dev/st0
for a tape drive. -
Replace restoration-path with the path to the directory where you want to restore the file system. For example,
/mnt/data/
. -
To restore a file system from an incremental (level 1 to level 9) backup, add the
-r
option. To restore a backup from a tape device that contains multiple backups, specify the backup using the
-S
or-L
options.The
-S
option lets you choose a backup by its session ID, while the-L
option lets you choose by the session label. To obtain the session ID and session labels, use thexfsrestore -I
command.Replace session-id with the session ID of the backup. For example,
b74a3586-e52e-4a4a-8775-c3334fa8ea2c
. Replace session-label with the session label of the backup. For example,my_backup_session_label
.To use
xfsrestore
interactively, use the-i
option.The interactive dialog begins after
xfsrestore
finishes reading the specified device. Available commands in the interactivexfsrestore
shell includecd
,ls
,add
,delete
, andextract
; for a complete list of commands, use thehelp
command.
-
Replace backup-location with the location of the backup. This can be a regular file, a tape drive, or a remote tape device. For example,
Example 12.1. Restoring Multiple XFS File Systems
To restore the XFS backup files and save their content into directories under
/mnt/
:# xfsrestore -f /backup-files/boot.xfsdump /mnt/boot/ # xfsrestore -f /backup-files/data.xfsdump /mnt/data/
To restore from a tape device containing multiple backups, specify each backup by its session label or session ID:
# xfsrestore -L "backup_boot" -f /dev/st0 /mnt/boot/ # xfsrestore -S "45e9af35-efd2-4244-87bc-4762e476cbab" \ -f /dev/st0 /mnt/data/
Additional resources
-
xfsrestore(8)
man page on your system
12.3. Informational messages when restoring an XFS backup from a tape
When restoring a backup from a tape with backups from multiple file systems, the xfsrestore
utility might issue messages. The messages inform you whether a match of the requested backup has been found when xfsrestore
examines each backup on the tape in sequential order. For example:
xfsrestore: preparing drive xfsrestore: examining media file 0 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) xfsrestore: examining media file 1 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) [...]
The informational messages keep appearing until the matching backup is found.
Chapter 13. Increasing the size of an XFS file system
As a system administrator, you can increase the size of an XFS file system to make a complete use of a larger storage capacity.
It is not currently possible to decrease the size of XFS file systems.
13.1. Increasing the size of an XFS file system with xfs_growfs
This procedure describes how to grow an XFS file system using the xfs_growfs
utility.
Prerequisites
- Ensure that the underlying block device is of an appropriate size to hold the resized file system later. Use the appropriate resizing methods for the affected block device.
- Mount the XFS file system.
Procedure
While the XFS file system is mounted, use the
xfs_growfs
utility to increase its size:# xfs_growfs file-system -D new-size
- Replace file-system with the mount point of the XFS file system.
With the
-D
option, replace new-size with the desired new size of the file system specified in the number of file system blocks.To find out the block size in kB of a given XFS file system, use the
xfs_info
utility:# xfs_info block-device ... data = bsize=4096 ...
-
Without the
-D
option,xfs_growfs
grows the file system to the maximum size supported by the underlying device.
Additional resources
-
xfs_growfs(8)
man page on your system.
Chapter 14. Configuring XFS error behavior
You can configure how an XFS file system behaves when it encounters different I/O errors.
14.1. Configurable error handling in XFS
The XFS file system responds in one of the following ways when an error occurs during an I/O operation:
XFS repeatedly retries the I/O operation until the operation succeeds or XFS reaches a set limit.
The limit is based either on a maximum number of retries or a maximum time for retries.
- XFS considers the error permanent and stops the operation on the file system.
You can configure how XFS reacts to the following error conditions:
EIO
- Error when reading or writing
ENOSPC
- No space left on the device
ENODEV
- Device cannot be found
You can set the maximum number of retries and the maximum time in seconds until XFS considers an error permanent. XFS stops retrying the operation when it reaches either of the limits.
You can also configure XFS so that when unmounting a file system, XFS immediately cancels the retries regardless of any other configuration. This configuration enables the unmount operation to succeed despite persistent errors.
Default behavior
The default behavior for each XFS error condition depends on the error context. Some XFS errors such as ENODEV
are considered to be fatal and unrecoverable, regardless of the retry count. Their default retry limit is 0.
14.2. Configuration files for specific and undefined XFS error conditions
The following directories store configuration files that control XFS error behavior for different error conditions:
/sys/fs/xfs/device/error/metadata/EIO/
-
For the
EIO
error condition /sys/fs/xfs/device/error/metadata/ENODEV/
-
For the
ENODEV
error condition /sys/fs/xfs/device/error/metadata/ENOSPC/
-
For the
ENOSPC
error condition /sys/fs/xfs/device/error/default/
- Common configuration for all other, undefined error conditions
Each directory contains the following configuration files for configuring retry limits:
max_retries
- Controls the maximum number of times that XFS retries the operation.
retry_timeout_seconds
- Specifies the time limit in seconds after which XFS stops retrying the operation.
14.3. Setting XFS behavior for specific conditions
This procedure configures how XFS reacts to specific error conditions.
Procedure
Set the maximum number of retries, the retry time limit, or both:
To set the maximum number of retries, write the desired number to the
max_retries
file:# echo value > /sys/fs/xfs/device/error/metadata/condition/max_retries
To set the time limit, write the desired number of seconds to the
retry_timeout_seconds
file:# echo value > /sys/fs/xfs/device/error/metadata/condition/retry_timeout_second
value is a number between -1 and the maximum possible value of the C signed integer type. This is 2147483647 on 64-bit Linux.
In both limits, the value
-1
is used for continuous retries and0
to stop immediately.device is the name of the device, as found in the
/dev/
directory; for example,sda
.
14.4. Setting XFS behavior for undefined conditions
This procedure configures how XFS reacts to all undefined error conditions, which share a common configuration.
Procedure
Set the maximum number of retries, the retry time limit, or both:
To set the maximum number of retries, write the desired number to the
max_retries
file:# echo value > /sys/fs/xfs/device/error/metadata/default/max_retries
To set the time limit, write the desired number of seconds to the
retry_timeout_seconds
file:# echo value > /sys/fs/xfs/device/error/metadata/default/retry_timeout_seconds
value is a number between -1 and the maximum possible value of the C signed integer type. This is 2147483647 on 64-bit Linux.
In both limits, the value
-1
is used for continuous retries and0
to stop immediately.device is the name of the device, as found in the
/dev/
directory; for example,sda
.
14.5. Setting the XFS unmount behavior
This procedure configures how XFS reacts to error conditions when unmounting the file system.
If you set the fail_at_unmount
option in the file system, it overrides all other error configurations during unmount, and immediately unmounts the file system without retrying the I/O operation. This allows the unmount operation to succeed even in case of persistent errors.
You cannot change the fail_at_unmount
value after the unmount process starts, because the unmount process removes the configuration files from the sysfs
interface for the respective file system. You must configure the unmount behavior before the file system starts unmounting.
Procedure
Enable or disable the
fail_at_unmount
option:To cancel retrying all operations when the file system unmounts, enable the option:
# echo 1 > /sys/fs/xfs/device/error/fail_at_unmount
To respect the
max_retries
andretry_timeout_seconds
retry limits when the file system unmounts, disable the option:# echo 0 > /sys/fs/xfs/device/error/fail_at_unmount
device is the name of the device, as found in the
/dev/
directory; for example,sda
.
Chapter 15. Checking and repairing a file system
RHEL provides file system administration utilities which are capable of checking and repairing file systems. These tools are often referred to as fsck
tools, where fsck
is a shortened version of file system check. In most cases, these utilities are run automatically during system boot, if needed, but can also be manually invoked if required.
File system checkers guarantee only metadata consistency across the file system. They have no awareness of the actual data contained within the file system and are not data recovery tools.
15.1. Scenarios that require a file system check
The relevant fsck
tools can be used to check your system if any of the following occurs:
- System fails to boot
- Files on a specific disk become corrupt
- The file system shuts down or changes to read-only due to inconsistencies
- A file on the file system is inaccessible
File system inconsistencies can occur for various reasons, including but not limited to hardware errors, storage administration errors, and software bugs.
File system check tools cannot repair hardware problems. A file system must be fully readable and writable if repair is to operate successfully. If a file system was corrupted due to a hardware error, the file system must first be moved to a good disk, for example with the dd(8)
utility.
For journaling file systems, all that is normally required at boot time is to replay the journal if required and this is usually a very short operation.
However, if a file system inconsistency or corruption occurs, even for journaling file systems, then the file system checker must be used to repair the file system.
It is possible to disable file system check at boot by setting the sixth field in /etc/fstab
to 0
. However, Red Hat does not recommend doing so unless you are having issues with fsck
at boot time, for example with extremely large or remote file systems.
Additional resources
-
fstab(5)
,fsck(8)
, anddd(8)
man pages on your system
15.2. Potential side effects of running fsck
Generally, running the file system check and repair tool can be expected to automatically repair at least some of the inconsistencies it finds. In some cases, the following issues can arise:
- Severely damaged inodes or directories may be discarded if they cannot be repaired.
- Significant changes to the file system may occur.
To ensure that unexpected or undesirable changes are not permanently made, ensure you follow any precautionary steps outlined in the procedure.
15.3. Error-handling mechanisms in XFS
This section describes how XFS handles various kinds of errors in the file system.
Unclean unmounts
Journalling maintains a transactional record of metadata changes that happen on the file system.
In the event of a system crash, power failure, or other unclean unmount, XFS uses the journal (also called log) to recover the file system. The kernel performs journal recovery when mounting the XFS file system.
Corruption
In this context, corruption means errors on the file system caused by, for example:
- Hardware faults
- Bugs in storage firmware, device drivers, the software stack, or the file system itself
- Problems that cause parts of the file system to be overwritten by something outside of the file system
When XFS detects corruption in the file system or the file-system metadata, it may shut down the file system and report the incident in the system log. Note that if the corruption occurred on the file system hosting the /var
directory, these logs will not be available after a reboot.
Example 15.1. System log entry reporting an XFS corruption
# dmesg --notime | tail -15 XFS (loop0): Mounting V5 Filesystem XFS (loop0): Metadata CRC error detected at xfs_agi_read_verify+0xcb/0xf0 [xfs], xfs_agi block 0x2 XFS (loop0): Unmount and run xfs_repair XFS (loop0): First 128 bytes of corrupted metadata buffer: 00000000027b3b56: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000005f9abc7a: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000005b0aef35: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000000da9d2ded: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000001e265b07: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000006a40df69: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000000b272907: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000000e484aac5: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ XFS (loop0): metadata I/O error in "xfs_trans_read_buf_map" at daddr 0x2 len 1 error 74 XFS (loop0): xfs_imap_lookup: xfs_ialloc_read_agi() returned error -117, agno 0 XFS (loop0): Failed to read root inode 0x80, error 11
User-space utilities usually report the Input/output error message when trying to access a corrupted XFS file system. Mounting an XFS file system with a corrupted log results in a failed mount and the following error message:
mount: /mount-point: mount(2) system call failed: Structure needs cleaning.
You must manually use the xfs_repair
utility to repair the corruption.
Additional resources
-
xfs_repair(8)
man page on your system
15.4. Checking an XFS file system with xfs_repair
Perform a read-only check of an XFS file system by using the xfs_repair utility. Unlike other file system repair utilities, xfs_repair
does not run at boot time, even when an XFS file system was not cleanly unmounted. In case of an unclean unmount, XFS simply replays the log at mount time, ensuring a consistent file system; xfs_repair
cannot repair an XFS file system with a dirty log without remounting it first.
Although an fsck.xfs
binary is present in the xfsprogs
package, this is present only to satisfy initscripts
that look for an fsck.file
system binary at boot time. fsck.xfs
immediately exits with an exit code of 0.
Procedure
Replay the log by mounting and unmounting the file system:
# mount file-system # umount file-system
NoteIf the mount fails with a structure needs cleaning error, the log is corrupted and cannot be replayed. The dry run should discover and report more on-disk corruption as a result.
Use the
xfs_repair
utility to perform a dry run to check the file system. Any errors are printed and an indication of the actions that would be taken, without modifying the file system.# xfs_repair -n block-device
Mount the file system:
# mount file-system
Additional resources
-
xfs_repair(8)
andxfs_metadump(8)
man pages on your system
15.5. Repairing an XFS file system with xfs_repair
This procedure repairs a corrupted XFS file system using the xfs_repair
utility.
Procedure
Create a metadata image prior to repair for diagnostic or testing purposes using the
xfs_metadump
utility. A pre-repair file system metadata image can be useful for support investigations if the corruption is due to a software bug. Patterns of corruption present in the pre-repair image can aid in root-cause analysis.Use the
xfs_metadump
debugging tool to copy the metadata from an XFS file system to a file. The resultingmetadump
file can be compressed using standard compression utilities to reduce the file size if largemetadump
files need to be sent to support.# xfs_metadump block-device metadump-file
Replay the log by remounting the file system:
# mount file-system # umount file-system
Use the
xfs_repair
utility to repair the unmounted file system:If the mount succeeded, no additional options are required:
# xfs_repair block-device
If the mount failed with the Structure needs cleaning error, the log is corrupted and cannot be replayed. Use the
-L
option (force log zeroing) to clear the log:WarningThis command causes all metadata updates in progress at the time of the crash to be lost, which might cause significant file system damage and data loss. This should be used only as a last resort if the log cannot be replayed.
# xfs_repair -L block-device
Mount the file system:
# mount file-system
Additional resources
-
xfs_repair(8)
man page on your system
15.6. Error handling mechanisms in ext2, ext3, and ext4
The ext2, ext3, and ext4 file systems use the e2fsck
utility to perform file system checks and repairs. The file names fsck.ext2
, fsck.ext3
, and fsck.ext4
are hardlinks to the e2fsck
utility. These binaries are run automatically at boot time and their behavior differs based on the file system being checked and the state of the file system.
A full file system check and repair is invoked for ext2, which is not a metadata journaling file system, and for ext4 file systems without a journal.
For ext3 and ext4 file systems with metadata journaling, the journal is replayed in userspace and the utility exits. This is the default action because journal replay ensures a consistent file system after a crash.
If these file systems encounter metadata inconsistencies while mounted, they record this fact in the file system superblock. If e2fsck
finds that a file system is marked with such an error, e2fsck
performs a full check after replaying the journal (if present).
Additional resources
-
fsck(8)
ande2fsck(8)
man pages on your system
15.7. Checking an ext2, ext3, or ext4 file system with e2fsck
This procedure checks an ext2, ext3, or ext4 file system using the e2fsck
utility.
Procedure
Replay the log by remounting the file system:
# mount file-system # umount file-system
Perform a dry run to check the file system.
# e2fsck -n block-device
NoteAny errors are printed and an indication of the actions that would be taken, without modifying the file system. Later phases of consistency checking may print extra errors as it discovers inconsistencies which would have been fixed in early phases if it were running in repair mode.
Additional resources
-
e2image(8)
ande2fsck(8)
man pages on your system
15.8. Repairing an ext2, ext3, or ext4 file system with e2fsck
This procedure repairs a corrupted ext2, ext3, or ext4 file system using the e2fsck
utility.
Procedure
Save a file system image for support investigations. A pre-repair file system metadata image can be useful for support investigations if the corruption is due to a software bug. Patterns of corruption present in the pre-repair image can aid in root-cause analysis.
NoteSeverely damaged file systems may cause problems with metadata image creation.
If you are creating the image for testing purposes, use the
-r
option to create a sparse file of the same size as the file system itself.e2fsck
can then operate directly on the resulting file.# e2image -r block-device image-file
If you are creating the image to be archived or provided for diagnostic, use the
-Q
option, which creates a more compact file format suitable for transfer.# e2image -Q block-device image-file
Replay the log by remounting the file system:
# mount file-system # umount file-system
Automatically repair the file system. If user intervention is required,
e2fsck
indicates the unfixed problem in its output and reflects this status in the exit code.# e2fsck -p block-device
Additional resources
-
e2image(8)
man page on your system -
e2fsck(8)
man page on your system
-
Chapter 16. Mounting file systems
As a system administrator, you can mount file systems on your system to access data on them.
16.1. The Linux mount mechanism
These are the basic concepts of mounting file systems on Linux.
On Linux, UNIX, and similar operating systems, file systems on different partitions and removable devices (CDs, DVDs, or USB flash drives for example) can be attached to a certain point (the mount point) in the directory tree, and then detached again. While a file system is mounted on a directory, the original content of the directory is not accessible.
Note that Linux does not prevent you from mounting a file system to a directory with a file system already attached to it.
When mounting, you can identify the device by:
-
a universally unique identifier (UUID): for example,
UUID=34795a28-ca6d-4fd8-a347-73671d0c19cb
-
a volume label: for example,
LABEL=home
-
a full path to a non-persistent block device: for example,
/dev/sda3
When you mount a file system using the mount
command without all required information, that is without the device name, the target directory, or the file system type, the mount
utility reads the content of the /etc/fstab
file to check if the given file system is listed there. The /etc/fstab
file contains a list of device names and the directories in which the selected file systems are set to be mounted as well as the file system type and mount options. Therefore, when mounting a file system that is specified in /etc/fstab
, the following command syntax is sufficient:
Mounting by the mount point:
# mount directory
Mounting by the block device:
# mount device
Additional resources
-
mount(8)
man page on your system - How to list persistent naming attributes such as the UUID.
16.2. Listing currently mounted file systems
List all currently mounted file systems on the command line by using the findmnt
utility.
Procedure
To list all mounted file systems, use the
findmnt
utility:$ findmnt
To limit the listed file systems only to a certain file system type, add the
--types
option:$ findmnt --types fs-type
For example:
Example 16.1. Listing only XFS file systems
$ findmnt --types xfs TARGET SOURCE FSTYPE OPTIONS / /dev/mapper/luks-5564ed00-6aac-4406-bfb4-c59bf5de48b5 xfs rw,relatime ├─/boot /dev/sda1 xfs rw,relatime └─/home /dev/mapper/luks-9d185660-7537-414d-b727-d92ea036051e xfs rw,relatime
Additional resources
-
findmnt(8)
man page on your system
16.3. Mounting a file system with mount
Mount a file system by using the mount
utility.
Prerequisites
Verify that no file system is already mounted on your chosen mount point:
$ findmnt mount-point
Procedure
To attach a certain file system, use the
mount
utility:# mount device mount-point
Example 16.2. Mounting an XFS file system
For example, to mount a local XFS file system identified by UUID:
# mount UUID=ea74bbec-536d-490c-b8d9-5b40bbd7545b /mnt/data
If
mount
cannot recognize the file system type automatically, specify it using the--types
option:# mount --types type device mount-point
Example 16.3. Mounting an NFS file system
For example, to mount a remote NFS file system:
# mount --types nfs4 host:/remote-export /mnt/nfs
Additional resources
-
mount(8)
man page on your system
16.4. Moving a mount point
Change the mount point of a mounted file system to a different directory by using the mount
utility.
Procedure
To change the directory in which a file system is mounted:
# mount --move old-directory new-directory
Example 16.4. Moving a home file system
For example, to move the file system mounted in the
/mnt/userdirs/
directory to the/home/
mount point:# mount --move /mnt/userdirs /home
Verify that the file system has been moved as expected:
$ findmnt $ ls old-directory $ ls new-directory
Additional resources
-
mount(8)
man page on your system
16.5. Unmounting a file system with umount
Unmount a file system by using the umount
utility.
Procedure
Try unmounting the file system using either of the following commands:
By mount point:
# umount mount-point
By device:
# umount device
If the command fails with an error similar to the following, it means that the file system is in use because of a process is using resources on it:
umount: /run/media/user/FlashDrive: target is busy.
If the file system is in use, use the
fuser
utility to determine which processes are accessing it. For example:$ fuser --mount /run/media/user/FlashDrive /run/media/user/FlashDrive: 18351
Afterwards, stop the processes using the file system and try unmounting it again.
16.6. Mounting and unmounting file systems in the web console
To be able to use partitions on RHEL systems, you need to mount a file system on the partition as a device.
You also can unmount a file system and the RHEL system will stop using it. Unmounting the file system enables you to delete, remove, or re-format devices.
Prerequisites
-
The
cockpit-storaged
package is installed on your system.
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
- If you want to unmount a file system, ensure that the system does not use any file, service, or application stored in the partition.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click the Storage tab.
- In the Storage table, select a volume from which you want to delete the partition.
- In the GPT partitions section, click the menu button, next to the partition whose file system you want to mount or unmount.
- Click or .
16.7. Common mount options
The following table lists the most common options of the mount
utility. You can apply these mount options using the following syntax:
# mount --options option1,option2,option3 device mount-point
Option | Description |
---|---|
| Enables asynchronous input and output operations on the file system. |
|
Enables the file system to be mounted automatically using the |
|
Provides an alias for the |
| Allows the execution of binary files on the particular file system. |
| Mounts an image as a loop device. |
|
Default behavior disables the automatic mount of the file system using the |
| Disallows the execution of binary files on the particular file system. |
| Disallows an ordinary user (that is, other than root) to mount and unmount the file system. |
| Remounts the file system in case it is already mounted. |
| Mounts the file system for reading only. |
| Mounts the file system for both reading and writing. |
| Allows an ordinary user (that is, other than root) to mount and unmount the file system. |
Chapter 17. Sharing a mount on multiple mount points
As a system administrator, you can duplicate mount points to make the file systems accessible from multiple directories.
17.2. Creating a private mount point duplicate
Duplicate a mount point as a private mount. File systems that you later mount under the duplicate or the original mount point are not reflected in the other.
Procedure
Create a virtual file system (VFS) node from the original mount point:
# mount --bind original-dir original-dir
Mark the original mount point as private:
# mount --make-private original-dir
Alternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-rprivate
option instead of--make-private
.Create the duplicate:
# mount --bind original-dir duplicate-dir
Example 17.1. Duplicating /media into /mnt as a private mount point
Create a VFS node from the
/media
directory:# mount --bind /media /media
Mark the
/media
directory as private:# mount --make-private /media
Create its duplicate in
/mnt
:# mount --bind /media /mnt
It is now possible to verify that
/media
and/mnt
share content but none of the mounts within/media
appear in/mnt
. For example, if the CD-ROM drive contains non-empty media and the/media/cdrom/
directory exists, use:# mount /dev/cdrom /media/cdrom # ls /media/cdrom EFI GPL isolinux LiveOS # ls /mnt/cdrom #
It is also possible to verify that file systems mounted in the
/mnt
directory are not reflected in/media
. For example, if a non-empty USB flash drive that uses the/dev/sdc1
device is plugged in and the/mnt/flashdisk/
directory is present, use:# mount /dev/sdc1 /mnt/flashdisk # ls /media/flashdisk # ls /mnt/flashdisk en-US publican.cfg
Additional resources
-
mount(8)
man page on your system
17.4. Creating a slave mount point duplicate
Duplicate a mount point as a slave
mount type. File systems that you later mount under the original mount point are reflected in the duplicate but not the other way around.
Procedure
Create a virtual file system (VFS) node from the original mount point:
# mount --bind original-dir original-dir
Mark the original mount point as shared:
# mount --make-shared original-dir
Alternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-rshared
option instead of--make-shared
.Create the duplicate and mark it as the
slave
type:# mount --bind original-dir duplicate-dir # mount --make-slave duplicate-dir
Example 17.3. Duplicating /media into /mnt as a slave mount point
This example shows how to get the content of the /media
directory to appear in /mnt
as well, but without any mounts in the /mnt
directory to be reflected in /media
.
Create a VFS node from the
/media
directory:# mount --bind /media /media
Mark the
/media
directory as shared:# mount --make-shared /media
Create its duplicate in
/mnt
and mark it asslave
:# mount --bind /media /mnt # mount --make-slave /mnt
Verify that a mount within
/media
also appears in/mnt
. For example, if the CD-ROM drive contains non-empty media and the/media/cdrom/
directory exists, use:# mount /dev/cdrom /media/cdrom # ls /media/cdrom EFI GPL isolinux LiveOS # ls /mnt/cdrom EFI GPL isolinux LiveOS
Also verify that file systems mounted in the
/mnt
directory are not reflected in/media
. For example, if a non-empty USB flash drive that uses the/dev/sdc1
device is plugged in and the/mnt/flashdisk/
directory is present, use:# mount /dev/sdc1 /mnt/flashdisk # ls /media/flashdisk # ls /mnt/flashdisk en-US publican.cfg
Additional resources
-
mount(8)
man page on your system
17.5. Preventing a mount point from being duplicated
Mark a mount point as unbindable so that it is not possible to duplicate it in another mount point.
Procedure
To change the type of a mount point to an unbindable mount, use:
# mount --bind mount-point mount-point # mount --make-unbindable mount-point
Alternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-runbindable
option instead of--make-unbindable
.Any subsequent attempt to make a duplicate of this mount fails with the following error:
# mount --bind mount-point duplicate-dir mount: wrong fs type, bad option, bad superblock on mount-point, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so
Example 17.4. Preventing /media from being duplicated
To prevent the
/media
directory from being shared, use:# mount --bind /media /media # mount --make-unbindable /media
Additional resources
-
mount(8)
man page on your system
Chapter 18. Persistently mounting file systems
As a system administrator, you can persistently mount file systems to configure non-removable storage.
18.1. The /etc/fstab file
Use the /etc/fstab
configuration file to control persistent mount points of file systems. Each line in the /etc/fstab
file defines a mount point of a file system.
It includes six fields separated by white space:
-
The block device identified by a persistent attribute or a path in the
/dev
directory. - The directory where the device will be mounted.
- The file system on the device.
-
Mount options for the file system, which includes the
defaults
option to mount the partition at boot time with default options. The mount option field also recognizes thesystemd
mount unit options in thex-systemd.option
format. -
Backup option for the
dump
utility. -
Check order for the
fsck
utility.
The systemd-fstab-generator
dynamically converts the entries from the /etc/fstab
file to the systemd-mount
units. The systemd
auto mounts LVM volumes from /etc/fstab
during manual activation unless the systemd-mount
unit is masked.
Example 18.1. The /boot
file system in /etc/fstab
Block device | Mount point | File system | Options | Backup | Check |
---|---|---|---|---|---|
|
|
|
|
|
|
The systemd
service automatically generates mount units from entries in /etc/fstab
.
Additional resources
-
fstab(5)
andsystemd.mount(5)
man pages on your system
18.2. Adding a file system to /etc/fstab
Configure persistent mount point for a file system in the /etc/fstab
configuration file.
Procedure
Find out the UUID attribute of the file system:
$ lsblk --fs storage-device
For example:
Example 18.2. Viewing the UUID of a partition
$ lsblk --fs /dev/sda1 NAME FSTYPE LABEL UUID MOUNTPOINT sda1 xfs Boot ea74bbec-536d-490c-b8d9-5b40bbd7545b /boot
If the mount point directory does not exist, create it:
# mkdir --parents mount-point
As root, edit the
/etc/fstab
file and add a line for the file system, identified by the UUID.For example:
Example 18.3. The /boot mount point in /etc/fstab
UUID=ea74bbec-536d-490c-b8d9-5b40bbd7545b /boot xfs defaults 0 0
Regenerate mount units so that your system registers the new configuration:
# systemctl daemon-reload
Try mounting the file system to verify that the configuration works:
# mount mount-point
Additional resources
Chapter 19. Mounting file systems on demand
As a system administrator, you can configure file systems, such as NFS, to mount automatically on demand.
19.1. The autofs service
The autofs
service can mount and unmount file systems automatically (on-demand), therefore saving system resources. It can be used to mount file systems such as NFS, AFS, SMBFS, CIFS, and local file systems.
One drawback of permanent mounting using the /etc/fstab
configuration is that, regardless of how infrequently a user accesses the mounted file system, the system must dedicate resources to keep the mounted file system in place. This might affect system performance when, for example, the system is maintaining NFS mounts to many systems at one time.
An alternative to /etc/fstab
is to use the kernel-based autofs
service. It consists of the following components:
- A kernel module that implements a file system, and
- A user-space service that performs all of the other functions.
Additional resources
-
autofs(8)
man page on your system
19.2. The autofs configuration files
This section describes the usage and syntax of configuration files used by the autofs
service.
The master map file
The autofs
service uses /etc/auto.master
(master map) as its default primary configuration file. This can be changed to use another supported network source and name using the autofs
configuration in the /etc/autofs.conf
configuration file in conjunction with the Name Service Switch (NSS) mechanism.
All on-demand mount points must be configured in the master map. Mount point, host name, exported directory, and options can all be specified in a set of files (or other supported network sources) rather than configuring them manually for each host.
The master map file lists mount points controlled by autofs
, and their corresponding configuration files or network sources known as automount maps. The format of the master map is as follows:
mount-point map-name options
The variables used in this format are:
- mount-point
-
The
autofs
mount point; for example,/mnt/data
. - map-file
- The map source file, which contains a list of mount points and the file system location from which those mount points should be mounted.
- options
- If supplied, these apply to all entries in the given map, if they do not themselves have options specified.
Example 19.1. The /etc/auto.master file
The following is a sample line from /etc/auto.master
file:
/mnt/data /etc/auto.data
Map files
Map files configure the properties of individual on-demand mount points.
The automounter creates the directories if they do not exist. If the directories exist before the automounter was started, the automounter will not remove them when it exits. If a timeout is specified, the directory is automatically unmounted if the directory is not accessed for the timeout period.
The general format of maps is similar to the master map. However, the options field appears between the mount point and the location instead of at the end of the entry as in the master map:
mount-point options location
The variables used in this format are:
- mount-point
-
This refers to the
autofs
mount point. This can be a single directory name for an indirect mount or the full path of the mount point for direct mounts. Each direct and indirect map entry key (mount-point) can be followed by a space separated list of offset directories (subdirectory names each beginning with/
) making them what is known as a multi-mount entry. - options
-
When supplied, these options are appended to the master map entry options, if any, or used instead of the master map options if the configuration entry
append_options
is set tono
. - location
-
This refers to the file system location such as a local file system path (preceded with the Sun map format escape character
:
for map names beginning with/
), an NFS file system or other valid file system location.
Example 19.2. A map file
The following is a sample from a map file; for example, /etc/auto.misc
:
payroll -fstype=nfs4 personnel:/exports/payroll sales -fstype=xfs :/dev/hda4
The first column in the map file indicates the autofs
mount point: sales
and payroll
from the server called personnel
. The second column indicates the options for the autofs
mount. The third column indicates the source of the mount.
Following the given configuration, the autofs
mount points will be /home/payroll
and /home/sales
. The -fstype=
option is often omitted and is not needed if the file system is NFS, including mounts for NFSv4 if the system default is NFSv4 for NFS mounts.
Using the given configuration, if a process requires access to an autofs
unmounted directory such as /home/payroll/2006/July.sxc
, the autofs
service automatically mounts the directory.
The amd map format
The autofs
service recognizes map configuration in the amd
format as well. This is useful if you want to reuse existing automounter configuration written for the am-utils
service, which has been removed from Red Hat Enterprise Linux.
However, Red Hat recommends using the simpler autofs
format described in the previous sections.
Additional resources
-
autofs(5)
,autofs.conf(5)
, andauto.master(5)
man pages on your system -
/usr/share/doc/autofs/README.amd-maps
file
19.3. Configuring autofs mount points
Configure on-demand mount points by using the autofs
service.
Prerequisites
Install the
autofs
package:# yum install autofs
Start and enable the
autofs
service:# systemctl enable --now autofs
Procedure
-
Create a map file for the on-demand mount point, located at
/etc/auto.identifier
. Replace identifier with a name that identifies the mount point. - In the map file, enter the mount point, options, and location fields as described in The autofs configuration files section.
- Register the map file in the master map file, as described in The autofs configuration files section.
Allow the service to re-read the configuration, so it can manage the newly configured
autofs
mount:# systemctl reload autofs.service
Try accessing content in the on-demand directory:
# ls automounted-directory
19.4. Automounting NFS server user home directories with autofs service
Configure the autofs service to mount user home directories automatically.
Prerequisites
- The autofs package is installed.
- The autofs service is enabled and running.
Procedure
Specify the mount point and location of the map file by editing the
/etc/auto.master
file on a server on which you need to mount user home directories. To do so, add the following line into the/etc/auto.master
file:/home /etc/auto.home
Create a map file with the name of
/etc/auto.home
on a server on which you need to mount user home directories, and edit the file with the following parameters:* -fstype=nfs,rw,sync host.example.com:/home/&
You can skip
fstype
parameter, as it isnfs
by default. For more information, seeautofs(5)
man page on your system.Reload the
autofs
service:# systemctl reload autofs
19.5. Overriding or augmenting autofs site configuration files
It is sometimes useful to override site defaults for a specific mount point on a client system.
Example 19.3. Initial conditions
For example, consider the following conditions:
Automounter maps are stored in NIS and the
/etc/nsswitch.conf
file has the following directive:automount: files nis
The
auto.master
file contains:+auto.master
The NIS
auto.master
map file contains:/home auto.home
The NIS
auto.home
map contains:beth fileserver.example.com:/export/home/beth joe fileserver.example.com:/export/home/joe * fileserver.example.com:/export/home/&
The
autofs
configuration optionBROWSE_MODE
is set toyes
:BROWSE_MODE="yes"
-
The file map
/etc/auto.home
does not exist.
Procedure
This section describes the examples of mounting home directories from a different server and augmenting auto.home
with only selected entries.
Example 19.4. Mounting home directories from a different server
Given the preceding conditions, let’s assume that the client system needs to override the NIS map auto.home
and mount home directories from a different server.
In this case, the client needs to use the following
/etc/auto.master
map:/home /etc/auto.home +auto.master
The
/etc/auto.home
map contains the entry:* host.example.com:/export/home/&
Because the automounter only processes the first occurrence of a mount point, the /home
directory contains the content of /etc/auto.home
instead of the NIS auto.home
map.
Example 19.5. Augmenting auto.home with only selected entries
Alternatively, to augment the site-wide auto.home
map with just a few entries:
Create an
/etc/auto.home
file map, and in it put the new entries. At the end, include the NISauto.home
map. Then the/etc/auto.home
file map looks similar to:mydir someserver:/export/mydir +auto.home
With these NIS
auto.home
map conditions, listing the content of the/home
directory outputs:$ ls /home beth joe mydir
This last example works as expected because autofs
does not include the contents of a file map of the same name as the one it is reading. As such, autofs
moves on to the next map source in the nsswitch
configuration.
19.6. Using LDAP to store automounter maps
Configure autofs
to store automounter maps in LDAP configuration rather than in autofs
map files.
Prerequisites
-
LDAP client libraries must be installed on all systems configured to retrieve automounter maps from LDAP. On Red Hat Enterprise Linux, the
openldap
package should be installed automatically as a dependency of theautofs
package.
Procedure
-
To configure LDAP access, modify the
/etc/openldap/ldap.conf
file. Ensure that theBASE
,URI
, andschema
options are set appropriately for your site. The most recently established schema for storing automount maps in LDAP is described by the
rfc2307bis
draft. To use this schema, set it in the/etc/autofs.conf
configuration file by removing the comment characters from the schema definition. For example:Example 19.6. Setting autofs configuration
DEFAULT_MAP_OBJECT_CLASS="automountMap" DEFAULT_ENTRY_OBJECT_CLASS="automount" DEFAULT_MAP_ATTRIBUTE="automountMapName" DEFAULT_ENTRY_ATTRIBUTE="automountKey" DEFAULT_VALUE_ATTRIBUTE="automountInformation"
Ensure that all other schema entries are commented in the configuration. The
automountKey
attribute of therfc2307bis
schema replaces thecn
attribute of therfc2307
schema. Following is an example of an LDAP Data Interchange Format (LDIF) configuration:Example 19.7. LDIF Configuration
# auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: top objectClass: automountMap automountMapName: auto.master # /home, auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: automount automountKey: /home automountInformation: auto.home # auto.home, example.com dn: automountMapName=auto.home,dc=example,dc=com objectClass: automountMap automountMapName: auto.home # foo, auto.home, example.com dn: automountKey=foo,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: foo automountInformation: filer.example.com:/export/foo # /, auto.home, example.com dn: automountKey=/,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: / automountInformation: filer.example.com:/export/&
Additional resources
19.7. Using systemd.automount to mount a file system on demand with /etc/fstab
Mount a file system on demand using the automount systemd units when mount point is defined in /etc/fstab
. You have to add an automount unit for each mount and enable it.
Procedure
Add desired fstab entry as documented in Persistently mounting file systems. For example:
/dev/disk/by-id/da875760-edb9-4b82-99dc-5f4b1ff2e5f4 /mount/point xfs defaults 0 0
-
Add
x-systemd.automount
to the options field of entry created in the previous step. Load newly created units so that your system registers the new configuration:
# systemctl daemon-reload
Start the automount unit:
# systemctl start mount-point.automount
Verification
Check that
mount-point.automount
is running:# systemctl status mount-point.automount
Check that automounted directory has desired content:
# ls /mount/point
Additional resources
-
systemd.automount(5)
andsystemd.mount(5)
man pages on your system - Managing systemd
19.8. Using systemd.automount to mount a file system on-demand with a mount unit
Mount a file system on-demand using the automount systemd units when mount point is defined by a mount unit. You have to add an automount unit for each mount and enable it.
Procedure
Create a mount unit. For example:
mount-point.mount [Mount] What=/dev/disk/by-uuid/f5755511-a714-44c1-a123-cfde0e4ac688 Where=/mount/point Type=xfs
-
Create a unit file with the same name as the mount unit, but with extension
.automount
. Open the file and create an
[Automount]
section. Set theWhere=
option to the mount path:[Automount] Where=/mount/point [Install] WantedBy=multi-user.target
Load newly created units so that your system registers the new configuration:
# systemctl daemon-reload
Enable and start the automount unit instead:
# systemctl enable --now mount-point.automount
Verification
Check that
mount-point.automount
is running:# systemctl status mount-point.automount
Check that automounted directory has desired content:
# ls /mount/point
Additional resources
-
systemd.automount(5)
andsystemd.mount(5)
man pages on your system - Managing systemd
Chapter 20. Using SSSD component from IdM to cache the autofs maps
The System Security Services Daemon (SSSD) is a system service to access remote service directories and authentication mechanisms. The data caching is useful in case of the slow network connection. To configure the SSSD service to cache the autofs map, follow the procedures below in this section.
20.1. Configuring autofs manually to use IdM server as an LDAP server
Configure autofs
to use IdM server as an LDAP server.
Procedure
Edit the
/etc/autofs.conf
file to specify the schema attributes thatautofs
searches for:# # Other common LDAP naming # map_object_class = "automountMap" entry_object_class = "automount" map_attribute = "automountMapName" entry_attribute = "automountKey" value_attribute = "automountInformation"
NoteUser can write the attributes in both lower and upper cases in the
/etc/autofs.conf
file.Optional: Specify the LDAP configuration. There are two ways to do this. The simplest is to let the automount service discover the LDAP server and locations on its own:
ldap_uri = "ldap:///dc=example,dc=com"
This option requires DNS to contain SRV records for the discoverable servers.
Alternatively, explicitly set which LDAP server to use and the base DN for LDAP searches:
ldap_uri = "ldap://ipa.example.com" search_base = "cn=location,cn=automount,dc=example,dc=com"
Edit the
/etc/autofs_ldap_auth.conf
file so that autofs allows client authentication with the IdM LDAP server.-
Change
authrequired
to yes. Set the principal to the Kerberos host principal for the IdM LDAP server, host/FQDN@REALM. The principal name is used to connect to the IdM directory as part of GSS client authentication.
<autofs_ldap_sasl_conf usetls="no" tlsrequired="no" authrequired="yes" authtype="GSSAPI" clientprinc="host/server.example.com@EXAMPLE.COM" />
For more information about host principal, see Using canonicalized DNS host names in IdM.
If necessary, run
klist -k
to get the exact host principal information.
-
Change
20.2. Configuring SSSD to cache autofs maps
The SSSD service can be used to cache autofs
maps stored on an IdM server without having to configure autofs
to use the IdM server at all.
Prerequisites
-
The
sssd
package is installed.
Procedure
Open the SSSD configuration file:
# vim /etc/sssd/sssd.conf
Add the
autofs
service to the list of services handled by SSSD.[sssd] domains = ldap services = nss,pam,
autofs
Create a new
[autofs]
section. You can leave this blank, because the default settings for anautofs
service work with most infrastructures.[nss] [pam] [sudo]
[autofs]
[ssh] [pac]For more information, see the
sssd.conf
man page on your system.Optional: Set a search base for the
autofs
entries. By default, this is the LDAP search base, but a subtree can be specified in theldap_autofs_search_base
parameter.[domain/EXAMPLE] ldap_search_base = "dc=example,dc=com" ldap_autofs_search_base = "ou=automount,dc=example,dc=com"
Restart SSSD service:
# systemctl restart sssd.service
Check the
/etc/nsswitch.conf
file, so that SSSD is listed as a source for automount configuration:automount:
sss
filesRestart
autofs
service:# systemctl restart autofs.service
Test the configuration by listing a user’s
/home
directory, assuming there is a master map entry for/home
:# ls /home/userName
If this does not mount the remote file system, check the
/var/log/messages
file for errors. If necessary, increase the debug level in the/etc/sysconfig/autofs
file by setting thelogging
parameter todebug
.
Chapter 21. Setting read-only permissions for the root file system
Sometimes, you need to mount the root file system (/
) with read-only permissions. Example use cases include enhancing security or ensuring data integrity after an unexpected system power-off.
21.1. Files and directories that always retain write permissions
For the system to function properly, some files and directories need to retain write permissions. When the root file system is mounted in read-only mode, these files are mounted in RAM using the tmpfs
temporary file system.
The default set of such files and directories is read from the /etc/rwtab
file. Note that the readonly-root
package is required to have this file present in your system.
dirs /var/cache/man dirs /var/gdm <content truncated> empty /tmp empty /var/cache/foomatic <content truncated> files /etc/adjtime files /etc/ntp.conf <content truncated>
Entries in the /etc/rwtab
file follow this format:
copy-method path
In this syntax:
- Replace copy-method with one of the keywords specifying how the file or directory is copied to tmpfs.
- Replace path with the path to the file or directory.
The /etc/rwtab
file recognizes the following ways in which a file or directory can be copied to tmpfs
:
empty
An empty path is copied to
tmpfs
. For example:empty /tmp
dirs
A directory tree is copied to
tmpfs
, empty. For example:dirs /var/run
files
A file or a directory tree is copied to
tmpfs
intact. For example:files /etc/resolv.conf
The same format applies when adding custom paths to /etc/rwtab.d/
.
21.2. Configuring the root file system to mount with read-only permissions on boot
With this procedure, the root file system is mounted read-only on all following boots.
Procedure
In the
/etc/sysconfig/readonly-root
file, set theREADONLY
option toyes
to mount the file systems as read-only:READONLY=yes
Add the
ro
option in the root entry (/
) in the/etc/fstab
file:/dev/mapper/luks-c376919e... / xfs x-systemd.device-timeout=0,ro 1 1
Enable the
ro
kernel option:# grubby --update-kernel=ALL --args="ro"
Ensure that the
rw
kernel option is disabled:# grubby --update-kernel=ALL --remove-args="rw"
If you need to add files and directories to be mounted with write permissions in the
tmpfs
file system, create a text file in the/etc/rwtab.d/
directory and put the configuration there.For example, to mount the
/etc/example/file
file with write permissions, add this line to the/etc/rwtab.d/example
file:files /etc/example/file
ImportantChanges made to files and directories in
tmpfs
do not persist across boots.- Reboot the system to apply the changes.
Troubleshooting
If you mount the root file system with read-only permissions by mistake, you can remount it with read-and-write permissions again using the following command:
# mount -o remount,rw /
Chapter 22. Limiting storage space usage on XFS with quotas
You can restrict the amount of disk space available to users or groups by implementing disk quotas. You can also define a warning level at which system administrators are informed before a user consumes too much disk space or a partition becomes full.
The XFS quota subsystem manages limits on disk space (blocks) and file (inode) usage. XFS quotas control or report on usage of these items on a user, group, or directory or project level. Group and project quotas are only mutually exclusive on older non-default XFS disk formats.
When managing on a per-directory or per-project basis, XFS manages the disk usage of directory hierarchies associated with a specific project.
22.1. Disk quotas
In most computing environments, disk space is not infinite. The quota subsystem provides a mechanism to control usage of disk space.
You can configure disk quotas for individual users as well as user groups on the local file systems. This makes it possible to manage the space allocated for user-specific files (such as email) separately from the space allocated to the projects that a user works on. The quota subsystem warns users when they exceed their allotted limit, but allows some extra space for current work (hard limit/soft limit).
If quotas are implemented, you need to check if the quotas are exceeded and make sure the quotas are accurate. If users repeatedly exceed their quotas or consistently reach their soft limits, a system administrator can either help the user determine how to use less disk space or increase the user’s disk quota.
You can set quotas to control:
- The number of consumed disk blocks.
- The number of inodes, which are data structures that contain information about files in UNIX file systems. Because inodes store file-related information, this allows control over the number of files that can be created.
22.2. The xfs_quota
tool
You can use the xfs_quota
tool to manage quotas on XFS file systems. In addition, you can use XFS file systems with limit enforcement turned off as an effective disk usage accounting system.
The XFS quota system differs from other file systems in a number of ways. Most importantly, XFS considers quota information as file system metadata and uses journaling to provide a higher level guarantee of consistency.
Additional resources
-
xfs_quota(8)
man page on your system
22.3. File system quota management in XFS
The XFS quota subsystem manages limits on disk space (blocks) and file (inode) usage. XFS quotas control or report on usage of these items on a user, group, or directory or project level. Group and project quotas are only mutually exclusive on older non-default XFS disk formats.
When managing on a per-directory or per-project basis, XFS manages the disk usage of directory hierarchies associated with a specific project.
22.4. Enabling disk quotas for XFS
Enable disk quotas for users, groups, and projects on an XFS file system. Once quotas are enabled, the xfs_quota
tool can be used to set limits and report on disk usage.
Procedure
Enable quotas for users:
# mount -o uquota /dev/xvdb1 /xfs
Replace
uquota
withuqnoenforce
to allow usage reporting without enforcing any limits.Enable quotas for groups:
# mount -o gquota /dev/xvdb1 /xfs
Replace
gquota
withgqnoenforce
to allow usage reporting without enforcing any limits.Enable quotas for projects:
# mount -o pquota /dev/xvdb1 /xfs
Replace
pquota
withpqnoenforce
to allow usage reporting without enforcing any limits.Alternatively, include the quota mount options in the
/etc/fstab
file. The following example shows entries in the/etc/fstab
file to enable quotas for users, groups, and projects, respectively, on an XFS file system. These examples also mount the file system with read/write permissions:# vim /etc/fstab /dev/xvdb1 /xfs xfs rw,quota 0 0 /dev/xvdb1 /xfs xfs rw,gquota 0 0 /dev/xvdb1 /xfs xfs rw,prjquota 0 0
Additional resources
-
mount(8)
andxfs_quota(8)
man pages on your system
22.5. Reporting XFS usage
Use the xfs_quota
tool to set limits and report on disk usage. By default, xfs_quota
is run interactively, and in basic mode. Basic mode subcommands simply report usage, and are available to all users.
Prerequisites
- Quotas have been enabled for the XFS file system. See Enabling disk quotas for XFS.
Procedure
Start the
xfs_quota
shell:# xfs_quota
Show usage and limits for the given user:
# xfs_quota> quota username
Show free and used counts for blocks and inodes:
# xfs_quota> df
Run the help command to display the basic commands available with
xfs_quota
.# xfs_quota> help
Specify
q
to exitxfs_quota
.# xfs_quota> q
Additional resources
-
xfs_quota(8)
man page on your system
22.6. Modifying XFS quota limits
Start the xfs_quota
tool with the -x
option to enable expert mode and run the administrator commands, which allow modifications to the quota system. The subcommands of this mode allow actual configuration of limits, and are available only to users with elevated privileges.
Prerequisites
- Quotas have been enabled for the XFS file system. See Enabling disk quotas for XFS.
Procedure
Start the
xfs_quota
shell with the-x
option to enable expert mode:# xfs_quota -x
Report quota information for a specific file system:
# xfs_quota> report /path
For example, to display a sample quota report for
/home
(on/dev/blockdevice
), use the commandreport -h /home
. This displays output similar to the following:User quota on /home (/dev/blockdevice) Blocks User ID Used Soft Hard Warn/Grace ---------- --------------------------------- root 0 0 0 00 [------] testuser 103.4G 0 0 00 [------]
Modify quota limits:
# xfs_quota> limit isoft=500m ihard=700m user /path
For example, to set a soft and hard inode count limit of 500 and 700 respectively for user
john
, whose home directory is/home/john
, use the following command:# xfs_quota -x -c 'limit isoft=500 ihard=700 john' /home/
In this case, pass
mount_point
which is the mounted xfs file system.Run the help command to display the expert commands available with
xfs_quota -x
:# xfs_quota> help
Additional resources
-
xfs_quota(8)
man page on your system
22.7. Setting project limits for XFS
Configure limits for project-controlled directories.
Procedure
Add the project-controlled directories to
/etc/projects
. For example, the following adds the/var/log
path with a unique ID of 11 to/etc/projects
. Your project ID can be any numerical value mapped to your project.# echo 11:/var/log >> /etc/projects
Add project names to
/etc/projid
to map project IDs to project names. For example, the following associates a project calledlogfiles
with the project ID of 11 as defined in the previous step.# echo logfiles:11 >> /etc/projid
Initialize the project directory. For example, the following initializes the project directory
/var
:# xfs_quota -x -c 'project -s logfiles' /var
Configure quotas for projects with initialized directories:
# xfs_quota -x -c 'limit -p bhard=1g logfiles' /var
Additional resources
-
xfs_quota(8)
,projid(5)
, andprojects(5)
man pages on your system
Chapter 23. Limiting storage space usage on ext4 with quotas
You have to enable disk quotas on your system before you can assign them. You can assign disk quotas per user, per group or per project. However, if there is a soft limit set, you can exceed these quotas for a configurable period of time, known as the grace period.
23.1. Installing the quota tool
You must install the quota
RPM package to implement disk quotas.
Procedure
Install the
quota
package:# yum install quota
23.2. Enabling quota feature on file system creation
Enable quotas on file system creation.
Procedure
Enable quotas on file system creation:
# mkfs.ext4 -O quota /dev/sda
NoteOnly user and group quotas are enabled and initialized by default.
Change the defaults on file system creation:
# mkfs.ext4 -O quota -E quotatype=usrquota:grpquota:prjquota /dev/sda
Mount the file system:
# mount /dev/sda
Additional resources
-
ext4(5)
man page on your system.
23.3. Enabling quota feature on existing file systems
Enable the quota feature on existing file system by using the tune2fs
command.
Procedure
Unmount the file system:
# umount /dev/sda
Enable quotas on existing file system:
# tune2fs -O quota /dev/sda
NoteOnly user and group quotas are initialized by default.
Change the defaults:
# tune2fs -Q usrquota,grpquota,prjquota /dev/sda
Mount the file system:
# mount /dev/sda
Additional resources
-
ext4(5)
man page on your system.
23.4. Enabling quota enforcement
The quota accounting is enabled by default after mounting the file system without any additional options, but quota enforcement is not.
Prerequisites
- Quota feature is enabled and the default quotas are initialized.
Procedure
Enable quota enforcement by
quotaon
for the user quota:# mount /dev/sda /mnt
# quotaon /mnt
NoteThe quota enforcement can be enabled at mount time using
usrquota
,grpquota
, orprjquota
mount options.# mount -o usrquota,grpquota,prjquota /dev/sda /mnt
Enable user, group, and project quotas for all file systems:
# quotaon -vaugP
-
If neither of the
-u
,-g
, or-P
options are specified, only the user quotas are enabled. -
If only
-g
option is specified, only group quotas are enabled. -
If only
-P
option is specified, only project quotas are enabled.
-
If neither of the
Enable quotas for a specific file system, such as
/home
:# quotaon -vugP /home
Additional resources
-
quotaon(8)
man page on your system
23.5. Assigning quotas per user
The disk quotas are assigned to users with the edquota
command.
The text editor defined by the EDITOR
environment variable is used by edquota
. To change the editor, set the EDITOR
environment variable in your ~/.bash_profile
file to the full path of the editor of your choice.
Prerequisites
- User must exist prior to setting the user quota.
Procedure
Assign the quota for a user:
# edquota username
Replace username with the user to which you want to assign the quotas.
For example, if you enable a quota for the
/dev/sda
partition and execute the commandedquota testuser
, the following is displayed in the default editor configured on the system:Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/sda 44043 0 0 37418 0 0
Change the desired limits.
If any of the values are set to 0, limit is not set. Change them in the text editor.
For example, the following shows the soft and hard block limits for the testuser have been set to 50000 and 55000 respectively.
Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/sda 44043 50000 55000 37418 0 0
- The first column is the name of the file system that has a quota enabled for it.
- The second column shows how many blocks the user is currently using.
- The next two columns are used to set soft and hard block limits for the user on the file system.
-
The
inodes
column shows how many inodes the user is currently using. The last two columns are used to set the soft and hard inode limits for the user on the file system.
- The hard block limit is the absolute maximum amount of disk space that a user or group can use. Once this limit is reached, no further disk space can be used.
- The soft block limit defines the maximum amount of disk space that can be used. However, unlike the hard limit, the soft limit can be exceeded for a certain amount of time. That time is known as the grace period. The grace period can be expressed in seconds, minutes, hours, days, weeks, or months.
Verification
Verify that the quota for the user has been set:
# quota -v testuser Disk quotas for user testuser: Filesystem blocks quota limit grace files quota limit grace /dev/sda 1000* 1000 1000 0 0 0
23.6. Assigning quotas per group
You can assign quotas on a per-group basis.
Prerequisites
- Group must exist prior to setting the group quota.
Procedure
Set a group quota:
# edquota -g groupname
For example, to set a group quota for the
devel
group:# edquota -g devel
This command displays the existing quota for the group in the text editor:
Disk quotas for group devel (gid 505): Filesystem blocks soft hard inodes soft hard /dev/sda 440400 0 0 37418 0 0
- Modify the limits and save the file.
Verification
Verify that the group quota is set:
# quota -vg groupname
23.7. Assigning quotas per project
You can assign quotas per project.
Prerequisites
- Project quota is enabled on your file system.
Procedure
Add the project-controlled directories to
/etc/projects
. For example, the following adds the/var/log
path with a unique ID of 11 to/etc/projects
. Your project ID can be any numerical value mapped to your project.# echo 11:/var/log >> /etc/projects
Add project names to
/etc/projid
to map project IDs to project names. For example, the following associates a project calledLogs
with the project ID of 11 as defined in the previous step.# echo Logs:11 >> /etc/projid
Set the desired limits:
# edquota -P 11
NoteYou can choose the project either by its project ID (
11
in this case), or by its name (Logs
in this case).Using
quotaon
, enable quota enforcement:
Verification
Verify that the project quota is set:
# quota -vP 11
NoteYou can verify either by the project ID, or by the project name.
Additional resources
-
edquota(8)
,projid(5)
, andprojects(5)
man pages on your system
23.8. Setting the grace period for soft limits
If a given quota has soft limits, you can edit the grace period, which is the amount of time for which a soft limit can be exceeded. You can set the grace period for users, groups, or projects.
Procedure
Edit the grace period:
# edquota -t
While other edquota
commands operate on quotas for a particular user, group, or project, the -t
option operates on every file system with quotas enabled.
Additional resources
-
edquota(8)
man page on your system
23.9. Turning file system quotas off
Use quotaoff
to turn disk quota enforcement off on the specified file systems. Quota accounting stays enabled after executing this command.
Procedure
To turn all user and group quotas off:
# quotaoff -vaugP
-
If neither of the
-u
,-g
, or-P
options are specified, only the user quotas are disabled. -
If only
-g
option is specified, only group quotas are disabled. -
If only
-P
option is specified, only project quotas are disabled. -
The
-v
switch causes verbose status information to display as the command executes.
-
If neither of the
Additional resources
-
quotaoff(8)
man page on your system
23.10. Reporting on disk quotas
Create a disk quota report by using the repquota
utility.
Procedure
Run the
repquota
command:# repquota
For example, the command
repquota /dev/sda
produces this output:*** Report for user quotas on device /dev/sda Block grace time: 7days; Inode grace time: 7days Block limits File limits User used soft hard grace used soft hard grace ---------------------------------------------------------------------- root -- 36 0 0 4 0 0 kristin -- 540 0 0 125 0 0 testuser -- 440400 500000 550000 37418 0 0
View the disk usage report for all quota-enabled file systems:
# repquota -augP
The --
symbol displayed after each user determines whether the block or inode limits have been exceeded. If either soft limit is exceeded, a +
character appears in place of the corresponding -
character. The first -
character represents the block limit, and the second represents the inode limit.
The grace
columns are normally blank. If a soft limit has been exceeded, the column contains a time specification equal to the amount of time remaining on the grace period. If the grace period has expired, none
appears in its place.
Additional resources
The repquota(8)
man page for more information.
Chapter 24. Discarding unused blocks
You can perform or schedule discard operations on block devices that support them. The block discard operation communicates to the underlying storage which filesystem blocks are no longer in use by the mounted filesystem. Block discard operations allow SSDs to optimize garbage collection routines, and they can inform thinly-provisioned storage to repurpose unused physical blocks.
Requirements
The block device underlying the file system must support physical discard operations.
Physical discard operations are supported if the value in the
/sys/block/<device>/queue/discard_max_bytes
file is not zero.
24.1. Types of block discard operations
You can run discard operations using different methods:
- Batch discard
- Is triggered explicitly by the user and discards all unused blocks in the selected file systems.
- Online discard
-
Is specified at mount time and triggers in real time without user intervention. Online discard operations discard only blocks that are transitioning from the
used
to thefree
state. - Periodic discard
-
Are batch operations that are run regularly by a
systemd
service.
All types are supported by the XFS and ext4 file systems.
Recommendations
Red Hat recommends that you use batch or periodic discard.
Use online discard only if:
- the system’s workload is such that batch discard is not feasible, or
- online discard operations are necessary to maintain performance.
24.2. Performing batch block discard
You can perform a batch block discard operation to discard unused blocks on a mounted file system.
Prerequisites
- The file system is mounted.
- The block device underlying the file system supports physical discard operations.
Procedure
Use the
fstrim
utility:To perform discard only on a selected file system, use:
# fstrim mount-point
To perform discard on all mounted file systems, use:
# fstrim --all
If you execute the fstrim
command on:
- a device that does not support discard operations, or
- a logical device (LVM or MD) composed of multiple devices, where any one of the device does not support discard operations,
the following message displays:
# fstrim /mnt/non_discard fstrim: /mnt/non_discard: the discard operation is not supported
Additional resources
-
fstrim(8)
man page on your system
24.3. Enabling online block discard
You can perform online block discard operations to automatically discard unused blocks on all supported file systems.
Procedure
Enable online discard at mount time:
When mounting a file system manually, add the
-o discard
mount option:# mount -o discard device mount-point
-
When mounting a file system persistently, add the
discard
option to the mount entry in the/etc/fstab
file.
Additional resources
-
mount(8)
andfstab(5)
man pages on your system
24.4. Enabling periodic block discard
You can enable a systemd
timer to regularly discard unused blocks on all supported file systems.
Procedure
Enable and start the
systemd
timer:# systemctl enable --now fstrim.timer Created symlink /etc/systemd/system/timers.target.wants/fstrim.timer → /usr/lib/systemd/system/fstrim.timer.
Verification
Verify the status of the timer:
# systemctl status fstrim.timer fstrim.timer - Discard unused blocks once a week Loaded: loaded (/usr/lib/systemd/system/fstrim.timer; enabled; vendor preset: disabled) Active: active (waiting) since Wed 2023-05-17 13:24:41 CEST; 3min 15s ago Trigger: Mon 2023-05-22 01:20:46 CEST; 4 days left Docs: man:fstrim May 17 13:24:41 localhost.localdomain systemd[1]: Started Discard unused blocks once a week.
Chapter 25. Setting up Stratis file systems
Stratis runs as a service to manage pools of physical storage devices, simplifying local storage management with ease of use while helping you set up and manage complex storage configurations.
Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
25.1. What is Stratis
Stratis is a local storage-management solution for Linux. It is focused on simplicity and ease of use, and gives you access to advanced storage features.
Stratis makes the following activities easier:
- Initial configuration of storage
- Making changes later
- Using advanced storage features
Stratis is a local storage management system that supports advanced storage features. The central concept of Stratis is a storage pool. This pool is created from one or more local disks or partitions, and file systems are created from the pool.
The pool enables many useful features, such as:
- File system snapshots
- Thin provisioning
- Tiering
- Encryption
Additional resources
25.2. Components of a Stratis volume
Learn about the components that comprise a Stratis volume.
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev
- Block devices, such as a disk or a disk partition.
pool
Composed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cache
target.Stratis creates a
/dev/stratis/my-pool/
directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystem
Each pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/dev/stratis/my-pool/my-fs
path.
Stratis uses many Device Mapper devices, which show up in dmsetup
listings and the /proc/partitions
file. Similarly, the lsblk
command output reflects the internal workings and layers of Stratis.
25.3. Block devices usable with Stratis
Storage devices that can be used with Stratis.
Supported devices
Stratis pools have been tested to work on these types of block devices:
- LUKS
- LVM logical volumes
- MD RAID
- DM Multipath
- iSCSI
- HDDs and SSDs
- NVMe devices
Unsupported devices
Because Stratis contains a thin-provisioning layer, Red Hat does not recommend placing a Stratis pool on block devices that are already thinly-provisioned.
25.4. Installing Stratis
Install the required packages for Stratis.
Procedure
Install packages that provide the Stratis service and command-line utilities:
# yum install stratisd stratis-cli
Verify that the
stratisd
service is enabled:# systemctl enable --now stratisd
25.5. Creating an unencrypted Stratis pool
You can create an unencrypted Stratis pool from one or more block devices.
Prerequisites
- Stratis is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - The block devices on which you are creating a Stratis pool are not in use and are not mounted.
- Each block device on which you are creating a Stratis pool is at least 1 GB.
-
On the IBM Z architecture, the
/dev/dasd*
block devices must be partitioned. Use the partition device for creating the Stratis pool.
For information about partitioning DASD devices, see Configuring a Linux instance on IBM Z
You cannot encrypt an unencrypted Stratis pool.
Procedure
Erase any file system, partition table, or RAID signatures that exist on each block device that you want to use in the Stratis pool:
# wipefs --all block-device
where
block-device
is the path to the block device; for example,/dev/sdb
.Create the new unencrypted Stratis pool on the selected block device:
# stratis pool create my-pool block-device
where
block-device
is the path to an empty or wiped block device.NoteSpecify multiple block devices on a single line:
# stratis pool create my-pool block-device-1 block-device-2
Verify that the new Stratis pool was created:
# stratis pool list
25.6. Creating an unencrypted Stratis pool by using the web console
You can use the web console to create an unencrypted Stratis pool from one or more block devices.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
-
The
stratisd
service is running. - The block devices on which you are creating a Stratis pool are not in use and are not mounted.
- Each block device on which you are creating a Stratis pool is at least 1 GB.
You cannot encrypt an unencrypted Stratis pool after it is created.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- In the Storage table, click the menu button.
From the drop-down menu, select Create Stratis pool.
In the Create Stratis pool dialog box, enter a name for the Stratis pool.
- Select the Block devices from which you want to create the Stratis pool.
- Optional: If you want to specify the maximum size for each file system that is created in pool, select Manage filesystem sizes.
- Click .
Verification
- Go to the Storage section and verify that you can see the new Stratis pool in the Devices table.
25.7. Creating an encrypted Stratis pool
To secure your data, you can create an encrypted Stratis pool from one or more block devices.
When you create an encrypted Stratis pool, the kernel keyring is used as the primary encryption mechanism. After subsequent system reboots this kernel keyring is used to unlock the encrypted Stratis pool.
When creating an encrypted Stratis pool from one or more block devices, note the following:
-
Each block device is encrypted using the
cryptsetup
library and implements theLUKS2
format. - Each Stratis pool can either have a unique key or share the same key with other pools. These keys are stored in the kernel keyring.
- The block devices that comprise a Stratis pool must be either all encrypted or all unencrypted. It is not possible to have both encrypted and unencrypted block devices in the same Stratis pool.
- Block devices added to the data tier of an encrypted Stratis pool are automatically encrypted.
Prerequisites
- Stratis v2.1.0 or later is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - The block devices on which you are creating a Stratis pool are not in use and are not mounted.
- The block devices on which you are creating a Stratis pool are at least 1GB in size each.
-
On the IBM Z architecture, the
/dev/dasd*
block devices must be partitioned. Use the partition in the Stratis pool.
For information about partitioning DASD devices, see link:Configuring a Linux instance on IBM Z.
Procedure
Erase any file system, partition table, or RAID signatures that exist on each block device that you want to use in the Stratis pool:
# wipefs --all block-device
where
block-device
is the path to the block device; for example,/dev/sdb
.If you have not created a key set already, run the following command and follow the prompts to create a key set to use for the encryption.
# stratis key set --capture-key key-description
where
key-description
is a reference to the key that gets created in the kernel keyring.Create the encrypted Stratis pool and specify the key description to use for the encryption. You can also specify the key path using the
--keyfile-path
option instead of using thekey-description
option.# stratis pool create --key-desc key-description my-pool block-device
where
key-description
- References the key that exists in the kernel keyring, which you created in the previous step.
my-pool
- Specifies the name of the new Stratis pool.
block-device
Specifies the path to an empty or wiped block device.
NoteSpecify multiple block devices on a single line:
# stratis pool create --key-desc key-description my-pool block-device-1 block-device-2
Verify that the new Stratis pool was created:
# stratis pool list
25.8. Creating an encrypted Stratis pool by using the web console
To secure your data, you can use the web console to create an encrypted Stratis pool from one or more block devices.
When creating an encrypted Stratis pool from one or more block devices, note the following:
- Each block device is encrypted using the cryptsetup library and implements the LUKS2 format.
- Each Stratis pool can either have a unique key or share the same key with other pools. These keys are stored in the kernel keyring.
- The block devices that comprise a Stratis pool must be either all encrypted or all unencrypted. It is not possible to have both encrypted and unencrypted block devices in the same Stratis pool.
- Block devices added to the data tier of an encrypted Stratis pool are automatically encrypted.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
- Stratis v2.1.0 or later is installed.
-
The
stratisd
service is running. - The block devices on which you are creating a Stratis pool are not in use and are not mounted.
- Each block device on which you are creating a Stratis pool is at least 1 GB.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- In the Storage table, click the menu button.
- From the drop-down menu, select Create Stratis pool.
In the Create Stratis pool dialog box, enter a name for the Stratis pool.
- Select the Block devices from which you want to create the Stratis pool.
Select the type of encryption, you can use a passphrase, a Tang keyserver, or both:
Passphrase:
- Enter a passphrase.
- Confirm the passphrase
Tang keyserver:
- Enter the keyserver address. For more information, see Deploying a Tang server with SELinux in enforcing mode.
- Optional: If you want to specify the maximum size for each file system that is created in pool, select Manage filesystem sizes.
- Click .
Verification
- Go to the Storage section and verify that you can see the new Stratis pool in the Devices table.
25.9. Renaming a Stratis pool by using the web console
You can use the web console to rename an existing Stratis pool.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
Stratis is installed.
The web console detects and installs Stratis by default. However, for manually installing Stratis, see Installing Stratis.
-
The
stratisd
service is running. - A Stratis pool is created.
Procedure
- Log in to the RHEL 8 web console.
- Click .
- In the Storage table, click the Stratis pool you want to rename.
On the Stratis pool page, click next to the Name field.
- In the Rename Stratis pool dialog box, enter a new name.
- Click .
25.10. Setting overprovisioning mode in Stratis filesystem
A storage stack can reach a state of overprovision. If the file system size becomes bigger than the pool backing it, the pool becomes full. To prevent this, disable overprovisioning, which ensures that the size of all filesystems on the pool does not exceed the available physical storage provided by the pool. If you use Stratis for critical applications or the root filesystem, this mode prevents certain failure cases.
If you enable overprovisioning, an API signal notifies you when your storage has been fully allocated. The notification serves as a warning to the user to inform them that when all the remaining pool space fills up, Stratis has no space left to extend to.
Prerequisites
- Stratis is installed. For more information, see Installing Stratis.
Procedure
To set up the pool correctly, you have two possibilities:
Create a pool from one or more block devices:
# stratis pool create pool-name /dev/sdb
Set overprovisioning mode in the existing pool:
# stratis pool overprovision pool-name <yes|no>
- If set to "yes", you enable overprovisioning to the pool. This means that the sum of the logical sizes of the Stratis filesystems, supported by the pool, can exceed the amount of available data space.
Verification
Run the following to view the full list of Stratis pools:
# stratis pool list Name Total Physical Properties UUID Alerts pool-name 1.42 TiB / 23.96 MiB / 1.42 TiB ~Ca,~Cr,~Op cb7cb4d8-9322-4ac4-a6fd-eb7ae9e1e540
-
Check if there is an indication of the pool overprovisioning mode flag in the
stratis pool list
output. The " ~ " is a math symbol for "NOT", so~Op
means no-overprovisioning. Optional: Run the following to check overprovisioning on a specific pool:
# stratis pool overprovision pool-name yes # stratis pool list Name Total Physical Properties UUID Alerts pool-name 1.42 TiB / 23.96 MiB / 1.42 TiB ~Ca,~Cr,~Op cb7cb4d8-9322-4ac4-a6fd-eb7ae9e1e540
Additional resources
25.11. Binding a Stratis pool to NBDE
Binding an encrypted Stratis pool to Network Bound Disk Encryption (NBDE) requires a Tang server. When a system containing the Stratis pool reboots, it connects with the Tang server to automatically unlock the encrypted pool without you having to provide the kernel keyring description.
Binding a Stratis pool to a supplementary Clevis encryption mechanism does not remove the primary kernel keyring encryption.
Prerequisites
- Stratis v2.3.0 or later is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created an encrypted Stratis pool, and you have the key description of the key that was used for the encryption. For more information, see Creating an encrypted Stratis pool.
- You can connect to the Tang server. For more information, see Deploying a Tang server with SELinux in enforcing mode
Procedure
Bind an encrypted Stratis pool to NBDE:
# stratis pool bind nbde --trust-url my-pool tang-server
where
my-pool
- Specifies the name of the encrypted Stratis pool.
tang-server
- Specifies the IP address or URL of the Tang server.
Additional resources
25.12. Binding a Stratis pool to TPM
When you bind an encrypted Stratis pool to the Trusted Platform Module (TPM) 2.0, the system containing the pool reboots, and the pool is automatically unlocked without you having to provide the kernel keyring description.
Prerequisites
- Stratis v2.3.0 or later is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created an encrypted Stratis pool. For more information, see Creating an encrypted Stratis pool.
Procedure
Bind an encrypted Stratis pool to TPM:
# stratis pool bind tpm my-pool key-description
where
my-pool
- Specifies the name of the encrypted Stratis pool.
key-description
- References the key that exists in the kernel keyring, which was generated when you created the encrypted Stratis pool.
25.13. Unlocking an encrypted Stratis pool with kernel keyring
After a system reboot, your encrypted Stratis pool or the block devices that comprise it might not be visible. You can unlock the pool using the kernel keyring that was used to encrypt the pool.
Prerequisites
- Stratis v2.1.0 is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created an encrypted Stratis pool. For more information, see Creating an encrypted Stratis pool.
Procedure
Re-create the key set using the same key description that was used previously:
# stratis key set --capture-key key-description
where key-description references the key that exists in the kernel keyring, which was generated when you created the encrypted Stratis pool.
Verify that the Stratis pool is visible:
# stratis pool list
25.14. Unbinding a Stratis pool from supplementary encryption
When you unbind an encrypted Stratis pool from a supported supplementary encryption mechanism, the primary kernel keyring encryption remains in place. This is not true for pools that are created with Clevis encryption from the start.
Prerequisites
- Stratis v2.3.0 or later is installed on your system. For more information, see Installing Stratis.
- You have created an encrypted Stratis pool. For more information, see Creating an encrypted Stratis pool.
- The encrypted Stratis pool is bound to a supported supplementary encryption mechanism.
Procedure
Unbind an encrypted Stratis pool from a supplementary encryption mechanism:
# stratis pool unbind clevis my-pool
where
my-pool
specifies the name of the Stratis pool you want to unbind.
Additional resources
25.15. Starting and stopping Stratis pool
You can start and stop Stratis pools. This gives you the option to dissasemble or bring down all the objects that were used to construct the pool, such as filesystems, cache devices, thin pool, and encrypted devices. Note that if the pool actively uses any device or filesystem, it might issue a warning and not be able to stop.
The stopped state is recorded in the pool’s metadata. These pools do not start on the following boot, until the pool receives a start command.
Prerequisites
- Stratis is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created either an unencrypted or an encrypted Stratis pool. See Creating an unencrypted Stratis pool
or Creating an encrypted Stratis pool.
Procedure
Use the following command to start the Stratis pool. The
--unlock-method
option specifies the method of unlocking the pool if it is encrypted:# stratis pool start pool-uuid --unlock-method <keyring|clevis>
Alternatively, use the following command to stop the Stratis pool. This tears down the storage stack but leaves all metadata intact:
# stratis pool stop pool-name
Verification
Use the following command to list all pools on the system:
# stratis pool list
Use the following command to list all not previously started pools. If the UUID is specified, the command prints detailed information about the pool corresponding to the UUID:
# stratis pool list --stopped --uuid UUID
25.16. Creating a Stratis file system
Create a Stratis file system on an existing Stratis pool.
Prerequisites
- Stratis is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis pool. See Creating an unencrypted Stratis pool
or Creating an encrypted Stratis pool.
Procedure
To create a Stratis file system on a pool, use:
# stratis filesystem create --size number-and-unit my-pool my-fs
where
number-and-unit
- Specifies the size of a file system. The specification format must follow the standard size specification format for input, that is B, KiB, MiB, GiB, TiB or PiB.
my-pool
- Specifies the name of the Stratis pool.
my-fs
Specifies an arbitrary name for the file system.
For example:
Example 25.1. Creating a Stratis file system
# stratis filesystem create --size 10GiB pool1 filesystem1
Verification
List file systems within the pool to check if the Stratis filesystem is created:
# stratis fs list my-pool
Additional resources
25.17. Creating a file system on a Stratis pool by using the web console
You can use the web console to create a file system on an existing Stratis pool.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
-
The
stratisd
service is running. - A Stratis pool is created.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- Click the Stratis pool on which you want to create a file system.
On the Stratis pool page, scroll to the Stratis filesystems section and click .
In the Create filesystem dialog box, enter a Name for the file system.
- Enter the Mount point for the file system.
- Select the Mount option.
- In the At boot drop-down menu, select when you want to mount your file system.
Create the file system:
- If you want to create and mount the file system, click .
- If you want to only create the file system, click .
Verification
- The new file system is visible on the Stratis pool page under the Stratis filesystems tab.
25.18. Mounting a Stratis file system
Mount an existing Stratis file system to access the content.
Prerequisites
- Stratis is installed. For more information, see Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis file system. For more information, see Creating a Stratis filesystem.
Procedure
To mount the file system, use the entries that Stratis maintains in the
/dev/stratis/
directory:# mount /dev/stratis/my-pool/my-fs mount-point
The file system is now mounted on the mount-point directory and ready to use.
Additional resources
25.19. Persistently mounting a Stratis file system
This procedure persistently mounts a Stratis file system so that it is available automatically after booting the system.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis file system. See Creating a Stratis filesystem.
Procedure
Determine the UUID attribute of the file system:
$ lsblk --output=UUID /dev/stratis/my-pool/my-fs
For example:
Example 25.2. Viewing the UUID of Stratis file system
$ lsblk --output=UUID /dev/stratis/my-pool/fs1 UUID a1f0b64a-4ebb-4d4e-9543-b1d79f600283
If the mount point directory does not exist, create it:
# mkdir --parents mount-point
As root, edit the
/etc/fstab
file and add a line for the file system, identified by the UUID. Usexfs
as the file system type and add thex-systemd.requires=stratisd.service
option.For example:
Example 25.3. The /fs1 mount point in /etc/fstab
UUID=a1f0b64a-4ebb-4d4e-9543-b1d79f600283 /fs1 xfs defaults,x-systemd.requires=stratisd.service 0 0
Regenerate mount units so that your system registers the new configuration:
# systemctl daemon-reload
Try mounting the file system to verify that the configuration works:
# mount mount-point
Additional resources
25.20. Setting up non-root Stratis filesystems in /etc/fstab using a systemd service
You can manage setting up non-root filesystems in /etc/fstab using a systemd service.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis file system. See Creating a Stratis filesystem.
Procedure
For all non-root Stratis filesystems, use:
# /dev/stratis/[STRATIS_SYMLINK] [MOUNT_POINT] xfs defaults, x-systemd.requires=stratis-fstab-setup@[POOL_UUID].service,x-systemd.after=stratis-stab-setup@[POOL_UUID].service <dump_value> <fsck_value>
Additional resources
Chapter 26. Extending a Stratis volume with additional block devices
You can attach additional block devices to a Stratis pool to provide more storage capacity for Stratis file systems.
Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
26.1. Components of a Stratis volume
Learn about the components that comprise a Stratis volume.
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev
- Block devices, such as a disk or a disk partition.
pool
Composed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cache
target.Stratis creates a
/dev/stratis/my-pool/
directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystem
Each pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/dev/stratis/my-pool/my-fs
path.
Stratis uses many Device Mapper devices, which show up in dmsetup
listings and the /proc/partitions
file. Similarly, the lsblk
command output reflects the internal workings and layers of Stratis.
26.2. Adding block devices to a Stratis pool
This procedure adds one or more block devices to a Stratis pool to be usable by Stratis file systems.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - The block devices that you are adding to the Stratis pool are not in use and not mounted.
- The block devices that you are adding to the Stratis pool are at least 1 GiB in size each.
Procedure
To add one or more block devices to the pool, use:
# stratis pool add-data my-pool device-1 device-2 device-n
Additional resources
-
stratis(8)
man page on your system
26.3. Adding a block device to a Stratis pool by using the web console
You can use the web console to add a block device to an existing Stratis pool. You can also add caches as a block device.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
-
The
stratisd
service is running. - A Stratis pool is created.
- The block devices on which you are creating a Stratis pool are not in use and are not mounted.
- Each block device on which you are creating a Stratis pool is at least 1 GB.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- In the Storage table, click the Stratis pool to which you want to add a block device.
On the Stratis pool page, click .
In the Add block devices dialog box, select the Tier, whether you want to add a block device as data or cache.
- Optional: If you are adding the block device to a Stratis pool that is encrypted with a passphrase, then you must enter the passphrase.
- Under Block devices, select the devices you want to add to the pool.
- Click .
26.4. Additional resources
Chapter 27. Monitoring Stratis file systems
As a Stratis user, you can view information about Stratis volumes on your system to monitor their state and free space.
Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
27.1. Stratis sizes reported by different utilities
This section explains the difference between Stratis sizes reported by standard utilities such as df
and the stratis
utility.
Standard Linux utilities such as df
report the size of the XFS file system layer on Stratis, which is 1 TiB. This is not useful information, because the actual storage usage of Stratis is less due to thin provisioning, and also because Stratis automatically grows the file system when the XFS layer is close to full.
Regularly monitor the amount of data written to your Stratis file systems, which is reported as the Total Physical Used value. Make sure it does not exceed the Total Physical Size value.
Additional resources
-
stratis(8)
man page on your system
27.2. Displaying information about Stratis volumes
This procedure lists statistics about your Stratis volumes, such as the total, used, and free size or file systems and block devices belonging to a pool.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running.
Procedure
To display information about all block devices used for Stratis on your system:
# stratis blockdev Pool Name Device Node Physical Size State Tier my-pool /dev/sdb 9.10 TiB In-use Data
To display information about all Stratis pools on your system:
# stratis pool Name Total Physical Size Total Physical Used my-pool 9.10 TiB 598 MiB
To display information about all Stratis file systems on your system:
# stratis filesystem Pool Name Name Used Created Device my-pool my-fs 546 MiB Nov 08 2018 08:03 /dev/stratis/my-pool/my-fs
Additional resources
-
stratis(8)
man page on your system
27.3. Viewing a Stratis pool by using the web console
You can use the web console to view an existing Stratis pool and the file systems it contains.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
-
The
stratisd
service is running. - You have an existing Stratis pool.
Procedure
- Log in to the RHEL 8 web console.
- Click .
In the Storage table, click the Stratis pool you want to view.
The Stratis pool page displays all the information about the pool and the file systems that you created in the pool.
27.4. Additional resources
Chapter 28. Using snapshots on Stratis file systems
You can use snapshots on Stratis file systems to capture file system state at arbitrary times and restore it in the future.
Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
28.1. Characteristics of Stratis snapshots
In Stratis, a snapshot is a regular Stratis file system created as a copy of another Stratis file system. The snapshot initially contains the same file content as the original file system, but can change as the snapshot is modified. Whatever changes you make to the snapshot will not be reflected in the original file system.
The current snapshot implementation in Stratis is characterized by the following:
- A snapshot of a file system is another file system.
- A snapshot and its origin are not linked in lifetime. A snapshotted file system can live longer than the file system it was created from.
- A file system does not have to be mounted to create a snapshot from it.
- Each snapshot uses around half a gigabyte of actual backing storage, which is needed for the XFS log.
28.2. Creating a Stratis snapshot
This procedure creates a Stratis file system as a snapshot of an existing Stratis file system.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis file system. See Creating a Stratis filesystem.
Procedure
To create a Stratis snapshot, use:
# stratis fs snapshot my-pool my-fs my-fs-snapshot
Additional resources
-
stratis(8)
man page on your system
28.3. Accessing the content of a Stratis snapshot
This procedure mounts a snapshot of a Stratis file system to make it accessible for read and write operations.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis snapshot. See Creating a Stratis filesystem.
Procedure
To access the snapshot, mount it as a regular file system from the
/dev/stratis/my-pool/
directory:# mount /dev/stratis/my-pool/my-fs-snapshot mount-point
Additional resources
- Mounting a Stratis file system
-
mount(8)
man page on your system
28.4. Reverting a Stratis file system to a previous snapshot
This procedure reverts the content of a Stratis file system to the state captured in a Stratis snapshot.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis snapshot. See Creating a Stratis snapshot.
Procedure
Optional: Back up the current state of the file system to be able to access it later:
# stratis filesystem snapshot my-pool my-fs my-fs-backup
Unmount and remove the original file system:
# umount /dev/stratis/my-pool/my-fs # stratis filesystem destroy my-pool my-fs
Create a copy of the snapshot under the name of the original file system:
# stratis filesystem snapshot my-pool my-fs-snapshot my-fs
Mount the snapshot, which is now accessible with the same name as the original file system:
# mount /dev/stratis/my-pool/my-fs mount-point
The content of the file system named my-fs is now identical to the snapshot my-fs-snapshot.
Additional resources
-
stratis(8)
man page on your system
28.5. Removing a Stratis snapshot
This procedure removes a Stratis snapshot from a pool. Data on the snapshot are lost.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis snapshot. See Creating a Stratis snapshot.
Procedure
Unmount the snapshot:
# umount /dev/stratis/my-pool/my-fs-snapshot
Destroy the snapshot:
# stratis filesystem destroy my-pool my-fs-snapshot
Additional resources
-
stratis(8)
man page on your system
28.6. Additional resources
Chapter 29. Removing Stratis file systems
You can remove an existing Stratis file system, or a Stratis pool, by destroying data on them.
Stratis is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
29.1. Components of a Stratis volume
Learn about the components that comprise a Stratis volume.
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev
- Block devices, such as a disk or a disk partition.
pool
Composed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cache
target.Stratis creates a
/dev/stratis/my-pool/
directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystem
Each pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/dev/stratis/my-pool/my-fs
path.
Stratis uses many Device Mapper devices, which show up in dmsetup
listings and the /proc/partitions
file. Similarly, the lsblk
command output reflects the internal workings and layers of Stratis.
29.2. Removing a Stratis file system
This procedure removes an existing Stratis file system. Data stored on it are lost.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. - You have created a Stratis file system. See Creating a Stratis filesystem.
Procedure
Unmount the file system:
# umount /dev/stratis/my-pool/my-fs
Destroy the file system:
# stratis filesystem destroy my-pool my-fs
Verify that the file system no longer exists:
# stratis filesystem list my-pool
Additional resources
-
stratis(8)
man page on your system
29.3. Deleting a file system from a Stratis pool by using the web console
You can use the web console to delete a file system from an existing Stratis pool.
Deleting a Stratis pool file system erases all the data it contains.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
Stratis is installed.
The web console detects and installs Stratis by default. However, for manually installing Stratis, see Installing Stratis.
-
The
stratisd
service is running. - You have an existing Stratis pool.
- You have created a file system on the Stratis pool.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- In the Storage table, click the Stratis pool from which you want to delete a file system.
On the Stratis pool page, scroll to the Stratis filesystems section and click the menu button next to the file system you want to delete.
From the drop-down menu, select
.- In the Confirm deletion dialog box, click .
29.4. Removing a Stratis pool
This procedure removes an existing Stratis pool. Data stored on it are lost.
Prerequisites
- Stratis is installed. See Installing Stratis.
-
The
stratisd
service is running. You have created a Stratis pool:
- To create an unencrypted pool, see Creating an unencrypted Stratis pool
- To create an encrypted pool, see Creating an encrypted Stratis pool.
Procedure
List file systems on the pool:
# stratis filesystem list my-pool
Unmount all file systems on the pool:
# umount /dev/stratis/my-pool/my-fs-1 \ /dev/stratis/my-pool/my-fs-2 \ /dev/stratis/my-pool/my-fs-n
Destroy the file systems:
# stratis filesystem destroy my-pool my-fs-1 my-fs-2
Destroy the pool:
# stratis pool destroy my-pool
Verify that the pool no longer exists:
# stratis pool list
Additional resources
-
stratis(8)
man page on your system
29.5. Deleting a Stratis pool by using the web console
You can use the web console to delete an existing Stratis pool.
Deleting a Stratis pool erases all the data it contains.
Prerequisites
You have installed the RHEL 8 web console.
For instructions, see Installing and enabling the web console.
-
The
stratisd
service is running. - You have an existing Stratis pool.
Procedure
Log in to the RHEL 8 web console.
For details, see Logging in to the web console.
- Click .
- In the Storage table, click the menu button, , next to the Stratis pool you want to delete.
- From the drop-down menu, select .
- In the Permanently delete pool dialog box, click .
29.6. Additional resources
Chapter 30. Getting started with an ext3 file system
As a system administrator, you can create, mount, resize, backup, and restore an ext3 file system. The ext3 file system is essentially an enhanced version of the ext2 file system.
30.1. Features of an ext3 file system
Following are the features of an ext3 file system:
Availability: After an unexpected power failure or system crash, file system check is not required due to the journaling provided. The default journal size takes about a second to recover, depending on the speed of the hardware
NoteThe only supported journaling mode in ext3 is
data=ordered
(default). For more information, see Is the EXT journaling option "data=writeback" supported in RHEL? Knowledgebase article.- Data Integrity: The ext3 file system prevents loss of data integrity during an unexpected power failure or system crash.
- Speed: Despite writing some data more than once, ext3 has a higher throughput in most cases than ext2 because ext3’s journaling optimizes hard drive head motion.
- Easy Transition: It is easy to migrate from ext2 to ext3 and gain the benefits of a robust journaling file system without reformatting.
Additional resources
-
ext3
man page on your system
30.2. Creating an ext3 file system
As a system administrator, you can create an ext3 file system on a block device using mkfs.ext3
command.
Prerequisites
- A partition on your disk. For information about creating MBR or GPT partitions, see Creating a partition table on a disk with parted.
.
+ Alternatively, use an LVM or MD volume.
Procedure
To create an ext3 file system:
For a regular-partition device, an LVM volume, an MD volume, or a similar device, use the following command:
# mkfs.ext3 /dev/block_device
Replace /dev/block_device with the path to a block device.
For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
. In general, the default options are optimal for most usage scenarios.For striped block devices (for example, RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry enhances the performance of an ext3 file system. For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command:
# mkfs.ext3 -E stride=16,stripe-width=64 /dev/block_device
In the given example:
- stride=value: Specifies the RAID chunk size
- stripe-width=value: Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
NoteTo specify a UUID when creating a file system:
# mkfs.ext3 -U UUID /dev/block_device
Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7
.Replace /dev/block_device with the path to an ext3 file system to have the UUID added to it: for example,
/dev/sda8
.To specify a label when creating a file system:
# mkfs.ext3 -L label-name /dev/block_device
To view the created ext3 file system:
# blkid
Additional resources
-
ext3
andmkfs.ext3
man pages on your system
30.3. Mounting an ext3 file system
As a system administrator, you can mount an ext3 file system using the mount
utility.
Prerequisites
- An ext3 file system. For information about creating an ext3 file system, see Creating an ext3 file system.
Procedure
To create a mount point to mount the file system:
# mkdir /mount/point
Replace /mount/point with the directory name where mount point of the partition must be created.
To mount an ext3 file system:
To mount an ext3 file system with no extra options:
# mount /dev/block_device /mount/point
- To mount the file system persistently, see Persistently mounting file systems.
To view the mounted file system:
# df -h
Additional resources
-
mount
,ext3
, andfstab
man pages on your system - Mounting file systems
30.4. Resizing an ext3 file system
As a system administrator, you can resize an ext3 file system using the resize2fs
utility. The resize2fs
utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:
-
s (sectors) -
512
byte sectors -
K (kilobytes) -
1,024
bytes -
M (megabytes) -
1,048,576
bytes -
G (gigabytes) -
1,073,741,824
bytes -
T (terabytes) -
1,099,511,627,776
bytes
Prerequisites
- An ext3 file system. For information about creating an ext3 file system, see Creating an ext3 file system.
- An underlying block device of an appropriate size to hold the file system after resizing.
Procedure
To resize an ext3 file system, take the following steps:
To shrink and grow the size of an unmounted ext3 file system:
# umount /dev/block_device # e2fsck -f /dev/block_device # resize2fs /dev/block_device size
Replace /dev/block_device with the path to the block device, for example
/dev/sdb1
.Replace size with the required resize value using
s
,K
,M
,G
, andT
suffixes.An ext3 file system may be grown while mounted using the
resize2fs
command:# resize2fs /mount/device size
NoteThe size parameter is optional (and often redundant) when expanding. The
resize2fs
automatically expands to fill the available space of the container, usually a logical volume or partition.
To view the resized file system:
# df -h
Additional resources
-
resize2fs
,e2fsck
, andext3
man pages on your system
Chapter 31. Getting started with an ext4 file system
As a system administrator, you can create, mount, resize, backup, and restore an ext4 file system. The ext4 file system is a scalable extension of the ext3 file system. With Red Hat Enterprise Linux 8, it can support a maximum individual file size of 16
terabytes, and file system to a maximum of 50
terabytes.
31.1. Features of an ext4 file system
Following are the features of an ext4 file system:
- Using extents: The ext4 file system uses extents, which improves performance when using large files and reduces metadata overhead for large files.
- Ext4 labels unallocated block groups and inode table sections accordingly, which allows the block groups and table sections to be skipped during a file system check. It leads to a quick file system check, which becomes more beneficial as the file system grows in size.
- Metadata checksum: By default, this feature is enabled in Red Hat Enterprise Linux 8.
Allocation features of an ext4 file system:
- Persistent pre-allocation
- Delayed allocation
- Multi-block allocation
- Stripe-aware allocation
-
Extended attributes (
xattr
): This allows the system to associate several additional name and value pairs per file. Quota journaling: This avoids the need for lengthy quota consistency checks after a crash.
NoteThe only supported journaling mode in ext4 is
data=ordered
(default). For more information, see Is the EXT journaling option "data=writeback" supported in RHEL? Knowledgebase article.- Subsecond timestamps — This gives timestamps to the subsecond.
Additional resources
-
ext4
man page on your system
31.2. Creating an ext4 file system
As a system administrator, you can create an ext4 file system on a block device using mkfs.ext4
command.
Prerequisites
- A partition on your disk. For information about creating MBR or GPT partitions, see Creating a partition table on a disk with parted.
- Alternatively, use an LVM or MD volume.
Procedure
To create an ext4 file system:
For a regular-partition device, an LVM volume, an MD volume, or a similar device, use the following command:
# mkfs.ext4 /dev/block_device
Replace /dev/block_device with the path to a block device.
For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
. In general, the default options are optimal for most usage scenarios.For striped block devices (for example, RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry enhances the performance of an ext4 file system. For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command:
# mkfs.ext4 -E stride=16,stripe-width=64 /dev/block_device
In the given example:
- stride=value: Specifies the RAID chunk size
- stripe-width=value: Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
NoteTo specify a UUID when creating a file system:
# mkfs.ext4 -U UUID /dev/block_device
Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7
.Replace /dev/block_device with the path to an ext4 file system to have the UUID added to it: for example,
/dev/sda8
.To specify a label when creating a file system:
# mkfs.ext4 -L label-name /dev/block_device
To view the created ext4 file system:
# blkid
Additional resources
-
ext4
andmkfs.ext4
man pages on your system
31.3. Mounting an ext4 file system
As a system administrator, you can mount an ext4 file system using the mount
utility.
Prerequisites
- An ext4 file system. For information about creating an ext4 file system, see Creating an ext4 file system.
Procedure
To create a mount point to mount the file system:
# mkdir /mount/point
Replace /mount/point with the directory name where mount point of the partition must be created.
To mount an ext4 file system:
To mount an ext4 file system with no extra options:
# mount /dev/block_device /mount/point
- To mount the file system persistently, see Persistently mounting file systems.
To view the mounted file system:
# df -h
Additional resources
-
mount
,ext4
, andfstab
man pages on your system - Mounting file systems
31.4. Resizing an ext4 file system
As a system administrator, you can resize an ext4 file system using the resize2fs
utility. The resize2fs
utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:
-
s (sectors) -
512
byte sectors -
K (kilobytes) -
1,024
bytes -
M (megabytes) -
1,048,576
bytes -
G (gigabytes) -
1,073,741,824
bytes -
T (terabytes) -
1,099,511,627,776
bytes
Prerequisites
- An ext4 file system. For information about creating an ext4 file system, see Creating an ext4 file system.
- An underlying block device of an appropriate size to hold the file system after resizing.
Procedure
To resize an ext4 file system, take the following steps:
To shrink and grow the size of an unmounted ext4 file system:
# umount /dev/block_device # e2fsck -f /dev/block_device # resize2fs /dev/block_device size
Replace /dev/block_device with the path to the block device, for example
/dev/sdb1
.Replace size with the required resize value using
s
,K
,M
,G
, andT
suffixes.An ext4 file system may be grown while mounted using the
resize2fs
command:# resize2fs /mount/device size
NoteThe size parameter is optional (and often redundant) when expanding. The
resize2fs
automatically expands to fill the available space of the container, usually a logical volume or partition.
To view the resized file system:
# df -h
Additional resources
-
resize2fs
,e2fsck
, andext4
man pages on your system
31.5. Comparison of tools used with ext4 and XFS
This section compares which tools to use to accomplish common tasks on the ext4 and XFS file systems.
Task | ext4 | XFS |
---|---|---|
Create a file system |
|
|
File system check |
|
|
Resize a file system |
|
|
Save an image of a file system |
|
|
Label or tune a file system |
|
|
Back up a file system |
|
|
Quota management |
|
|
File mapping |
|
|