Chapter 10. Getting started with XFS

This is an overview of how to create and maintain XFS file systems.

10.1. 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 (new in Red Hat Enterprise Linux 8)
  • 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.

10.2. 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.

10.2.1. Creating an XFS file system with mkfs.xfs

This procedure describes how to create an XFS file system on a block device.

Procedure

  1. 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.

    • 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 and sw parameters of the -d option. The su parameter specifies the RAID chunk size, and the sw parameter specifies the number of data disks in the RAID device.

        For example: 

        # mkfs.xfs -d su=64k,sw=4 /dev/sda3

  2. Use the following command to wait for the system to register the new device node: 

    # udevadm settle

Additional resources

  • The mkfs.xfs(8) man page.

10.2.2. Creating an XFS file system on a block device using RHEL System Roles

This section describes how to create an XFS file system on a block device on multiple target machines using the storage role.

Prerequisites

  • An Ansible playbook that uses the storage role exists.

    For information on how to apply such a playbook, see Applying a role.

10.2.2.1. Example Ansible playbook to create an XFS file system on a block device

This section provides an example Ansible playbook. This playbook applies the storage role to create an XFS file system on a block device (/dev/sdb) using the default parameters.

Warning

The storage role can create file systems only on whole disks. Partitions are not supported. 

---
- hosts: all
  vars:
    storage_volumes:
      - name: barefs
        type: disk
        disks:
          - sdb
        fs_type: xfs
  roles:
    - rhel-system-roles.storage

The volume name (barefs in the example) is currently arbitrary. The volume is identified by the disk device listed under the disks: attribute.

XFS is the default file system type in RHEL 8, so fs_type: xfs can be omitted.

Note

To create a file system on a logical volume, do not provide the path to the LV device under the disks: attribute. Instead, provide the LVM setup including the enclosing volume group as described in Configuring and managing logical volumes.

10.2.2.2. Additional resources

10.3. 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.

10.3.1. 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

  • The xfsdump(8) man page.

10.3.2. 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 or 1 to 9 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.

Example 10.1. 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

  • The xfsdump(8) man page.

10.3.3. Additional resources

  • The xfsdump(8) man page.

10.4. 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.

10.4.1. Features of restoring XFS from backup

This section describes key concepts and features of restoring an XFS file system from backup with the xfsrestore utility.

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

  • The xfsrestore(8) man page.

10.4.2. 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

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 the xfsrestore -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 interactive xfsrestore shell include cd, ls, add, delete, and extract; for a complete list of commands, use the help command.

Example 10.2. 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

  • The xfsrestore(8) man page.

10.4.3. 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.

10.4.4. Additional resources

  • The xfsrestore(8) man page.

10.5. Increasing the size of an XFS file system

As a system administrator, you can increase the size of an XFS file system to utilize larger storage capacity.

Important

It is not currently possible to decrease the size of XFS file systems.

10.5.1. 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

  • The xfs_growfs(8) man page.

10.6. 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.

Taskext4XFS

Create a file system

mkfs.ext4

mkfs.xfs

File system check

e2fsck

xfs_repair

Resize a file system

resize2fs

xfs_growfs

Save an image of a file system

e2image

xfs_metadump and xfs_mdrestore

Label or tune a file system

tune2fs

xfs_admin

Back up a file system

dump and restore

xfsdump and xfsrestore

Quota management

quota

xfs_quota

File mapping

filefrag

xfs_bmap