XFS

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XFS is a high-performance journaling file system created by Silicon Graphics, Inc. XFS is particularly proficient at parallel IO due to its allocation group based design. This enables extreme scalability of IO threads, filesystem bandwidth, file and filesystem size when spanning multiple storage devices.

Installation

The tools to manage XFS partitions are in the xfsprogs package, which is included in the default base installation.

Data corruption

If for whatever reason you experience data corruption, you will need to repair the filesystem manually.

Repair XFS Filesystem

First unmount the XFS filesystem.

# umount /dev/sda3

Once unmounted, run the xfs_repair(8) tool.

# xfs_repair -v /dev/sda3

Online Metadata Checking (scrub)

Warning: This program is EXPERIMENTAL, which means that its behavior and interface could change at any time, see xfs_scrub(8).

xfs_scrub asks the kernel to scrub all metadata objects in the XFS filesystem. Metadata records are scanned for obviously bad values and then cross-referenced against other metadata. The goal is to establish a reasonable confidence about the consistency of the overall filesystem by examining the consistency of individual metadata records against the other metadata in the filesystem. Damaged metadata can be rebuilt from other metadata if there exists redundant data structures which are intact.

Enable/start xfs_scrub_all.timer to periodic check online metadata for all XFS filesystems.

Note: One may want to edit xfs_scrub_all.timer: the timer runs every Sunday at 3:10am and will be triggered immediately if it missed the last start time, i.e. due to the system being powered off.

Integrity

xfsprogs 3.2.0 has introduced a new on-disk format (v5) that includes a metadata checksum scheme called Self-Describing Metadata. Based upon CRC32 it provides for example additional protection against metadata corruption during unexpected power losses. Checksum is enabled by default when using xfsprogs 3.2.3 or later. If you need read-write mountable xfs for older kernel, It can be easily disabled using the -m crc=0 switch when calling mkfs.xfs(8).

# mkfs.xfs -m crc=0 /dev/target_partition

The XFS v5 on-disk format is considered stable for production workloads starting Linux Kernel 3.15.

Note: Unlike Btrfs and ZFS, the CRC32 checksum only applies to the metadata and not actual data.

Performance

For optimal speed, just create an XFS file system with:

# mkfs.xfs /dev/target_partition

Yep, so simple - since all of the "boost knobs" are already "on" by default.

Also see xfs(5) for details of all available mount options.

Tip: When using the XFS filesystem on RAID devices, performance improvements may be possible by using largeio, swalloc, increased logbsize and allocsize values, etc. The following articles may provide additional details about those flags:

Stripe size and width

If this filesystem will be on a striped RAID you can gain significant speed improvements by specifying the stripe size to the mkfs.xfs(8) command.

See How to calculate the correct sunit,swidth values for optimal performance

Access time

On some filesystems you can increase performance by adding the noatime mount option to the /etc/fstab file. For XFS filesystems the default atime behaviour is relatime, which has almost no overhead compared to noatime but still maintains sane atime values. All Linux filesystems use this as the default now (since around 2.6.30), but XFS has used relatime-like behaviour since 2006, so no-one should really need to ever use noatime on XFS for performance reasons.

Also, noatime implies nodiratime, so there is never a need to specify nodiratime when noatime is also specified.

Defragmentation

Although the extent-based nature of XFS and the delayed allocation strategy it uses significantly improves the file system's resistance to fragmentation problems, XFS provides a filesystem defragmentation utility (xfs_fsr, short for XFS filesystem reorganizer) that can defragment the files on a mounted and active XFS filesystem. It can be useful to view XFS fragmentation periodically.

xfs_fsr(8) improves the organization of mounted filesystems. The reorganization algorithm operates on one file at a time, compacting or otherwise improving the layout of the file extents (contiguous blocks of file data).

Inspect fragmentation levels

To see how much fragmentation your file system currently has:

# xfs_db -c frag -r /dev/sda3

Perform defragmentation

To begin defragmentation, use the xfs_fsr(8) command:

# xfs_fsr /dev/sda3

Free inode btree

Starting Linux 3.16, XFS has added a btree that tracks free inodes. It is equivalent to the existing inode allocation btree with the exception that the free inode btree tracks inode chunks with at least one free inode. The purpose is to improve lookups for free inode clusters for inode allocation. It improves performance on aged filesystems i.e. months or years down the track when you have added and removed millions of files to/from the filesystem. Using this feature does not impact overall filesystem reliability level or recovery capabilities.

This feature relies on the new v5 on-disk format that has been considered stable for production workloads starting Linux Kernel 3.15. It does not change existing on-disk structures, but adds a new one that must remain consistent with the inode allocation btree; for this reason older kernels will only be able to mount read-only filesystems with the free inode btree feature.

The feature enabled by default when using xfsprogs 3.2.3 or later. If you need writable filesystem for older kernel, it can be disable with finobt=0 switch when formatting a XFS partition. You will need crc=0 together.

# mkfs.xfs -m crc=0,finobt=0 /dev/target_partition

or shortly (finobt depends crc)

# mkfs.xfs -m crc=0 /dev/target_partition

External XFS Journal

Using an external log (metadata journal) on for instance a SSD may be useful to improve performance [1]. See mkfs.xfs(8) for details about the logdev parameter.

Warning: Beware using flash-memory may wear-out the drive. See Improving performance#Reduce disk reads/writes for SSD wear-out details.

To reserve an external journal with a specified size when you create an XFS file system, specify the -l logdev=device,size=size option to the mkfs.xfs command. If you omit the size parameter, a journal size based on the size of the file system is used. To mount the XFS file system so that it uses the external journal, specify the -o logdev=device option to the mount command.

Troubleshooting

Root file system quota

XFS quota mount options (uquota, gquota, prjquota, etc.) fail during re-mount of the file system. To enable quota for root file system, the mount option must be passed to initramfs as a kernel parameter rootflags=. Subsequently, it should not be listed among mount options in /etc/fstab for the root (/) filesystem.

Note: There are some differences of XFS Quota compared to standard Linux Disk quota, this article http://inai.de/linux/adm_quota may be worth reading.

xfs_scrub_all fails if user "nobody" can not access the mountpoint

When running xfs_scrub_all, it will launch xfs_scrub@.service for each mounted XFS file system. The service is run as user nobody, so if nobody can not navigate to the directory, it will fail with the error:

xfs_scrub@mountpoint.service: Changing to the requested working directory failed: Permission denied
xfs_scrub@mountpoint.service: Failed at step CHDIR spawning /usr/bin/xfs_scrub: Permission denied
xfs_scrub@mountpoint.service: Main process exited, code=exited, status=200/CHDIR

To allow the service to run, change the permissions of the mountpoint so that user nobody has execute permissions.

See also