The SGI XFS Filesystem¶
XFS is a high performance journaling filesystem which originated on the SGI IRIX platform. It is completely multi-threaded, can support large files and large filesystems, extended attributes, variable block sizes, is extent based, and makes extensive use of Btrees (directories, extents, free space) to aid both performance and scalability.
Refer to the documentation at https://xfs.wiki.kernel.org/ for further details. This implementation is on-disk compatible with the IRIX version of XFS.
Mount Options¶
When mounting an XFS filesystem, the following options are accepted.
allocsize=size
Sets the buffered I/O end-of-file preallocation size when doing delayed allocation writeout (default size is 64KiB). Valid values for this option are page size (typically 4KiB) through to 1GiB, inclusive, in power-of-2 increments.
The default behaviour is for dynamic end-of-file preallocation size, which uses a set of heuristics to optimise the preallocation size based on the current allocation patterns within the file and the access patterns to the file. Specifying a fixed allocsize value turns off the dynamic behaviour.
attr2 or noattr2
The options enable/disable an «opportunistic» improvement to be made in the way inline extended attributes are stored on-disk. When the new form is used for the first time when attr2 is selected (either when setting or removing extended attributes) the on-disk superblock feature bit field will be updated to reflect this format being in use.
The default behaviour is determined by the on-disk feature bit indicating that attr2 behaviour is active. If either mount option is set, then that becomes the new default used by the filesystem.
CRC enabled filesystems always use the attr2 format, and so will reject the noattr2 mount option if it is set.
discard or nodiscard (default)
Enable/disable the issuing of commands to let the block device reclaim space freed by the filesystem. This is useful for SSD devices, thinly provisioned LUNs and virtual machine images, but may have a performance impact.
Note: It is currently recommended that you use the fstrim application to discard unused blocks rather than the discard mount option because the performance impact of this option is quite severe.
grpid/bsdgroups or nogrpid/sysvgroups (default)
These options define what group ID a newly created file gets. When grpid is set, it takes the group ID of the directory in which it is created; otherwise it takes the fsgid of the current process, unless the directory has the setgid bit set, in which case it takes the gid from the parent directory, and also gets the setgid bit set if it is a directory itself.
filestreams
Make the data allocator use the filestreams allocation mode across the entire filesystem rather than just on directories configured to use it.
ikeep or noikeep (default)
When ikeep is specified, XFS does not delete empty inode clusters and keeps them around on disk. When noikeep is specified, empty inode clusters are returned to the free space pool.
inode32 or inode64 (default)
When inode32 is specified, it indicates that XFS limits inode creation to locations which will not result in inode numbers with more than 32 bits of significance.
When inode64 is specified, it indicates that XFS is allowed to create inodes at any location in the filesystem, including those which will result in inode numbers occupying more than 32 bits of significance.
inode32 is provided for backwards compatibility with older systems and applications, since 64 bits inode numbers might cause problems for some applications that cannot handle large inode numbers. If applications are in use which do not handle inode numbers bigger than 32 bits, the inode32 option should be specified.
largeio or nolargeio (default)
If nolargeio is specified, the optimal I/O reported in st_blksize by stat(2) will be as small as possible to allow user applications to avoid inefficient read/modify/write I/O. This is typically the page size of the machine, as this is the granularity of the page cache.
If largeio is specified, a filesystem that was created with a swidth specified will return the swidth value (in bytes) in st_blksize . If the filesystem does not have a swidth specified but does specify an allocsize then allocsize (in bytes) will be returned instead. Otherwise the behaviour is the same as if nolargeio was specified.
logbufs=value
Set the number of in-memory log buffers. Valid numbers range from 2-8 inclusive.
The default value is 8 buffers.
If the memory cost of 8 log buffers is too high on small systems, then it may be reduced at some cost to performance on metadata intensive workloads. The logbsize option below controls the size of each buffer and so is also relevant to this case.
logbsize=value
Set the size of each in-memory log buffer. The size may be specified in bytes, or in kilobytes with a «k» suffix. Valid sizes for version 1 and version 2 logs are 16384 (16k) and 32768 (32k). Valid sizes for version 2 logs also include 65536 (64k), 131072 (128k) and 262144 (256k). The logbsize must be an integer multiple of the log stripe unit configured at mkfs(8) time.
The default value for version 1 logs is 32768, while the default value for version 2 logs is MAX(32768, log_sunit).
logdev=device and rtdev=device
Use an external log (metadata journal) and/or real-time device. An XFS filesystem has up to three parts: a data section, a log section, and a real-time section. The real-time section is optional, and the log section can be separate from the data section or contained within it.
noalign
Data allocations will not be aligned at stripe unit boundaries. This is only relevant to filesystems created with non-zero data alignment parameters ( sunit , swidth ) by mkfs(8).
norecovery
The filesystem will be mounted without running log recovery. If the filesystem was not cleanly unmounted, it is likely to be inconsistent when mounted in norecovery mode. Some files or directories may not be accessible because of this. Filesystems mounted norecovery must be mounted read-only or the mount will fail.
nouuid
Don’t check for double mounted file systems using the file system uuid . This is useful to mount LVM snapshot volumes, and often used in combination with norecovery for mounting read-only snapshots.
noquota
Forcibly turns off all quota accounting and enforcement within the filesystem.
uquota/usrquota/uqnoenforce/quota
User disk quota accounting enabled, and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
gquota/grpquota/gqnoenforce
Group disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
pquota/prjquota/pqnoenforce
Project disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details.
sunit=value and swidth=value
Used to specify the stripe unit and width for a RAID device or a stripe volume. «value» must be specified in 512-byte block units. These options are only relevant to filesystems that were created with non-zero data alignment parameters.
The sunit and swidth parameters specified must be compatible with the existing filesystem alignment characteristics. In general, that means the only valid changes to sunit are increasing it by a power-of-2 multiple. Valid swidth values are any integer multiple of a valid sunit value.
Typically the only time these mount options are necessary if after an underlying RAID device has had it’s geometry modified, such as adding a new disk to a RAID5 lun and reshaping it.
swalloc
Data allocations will be rounded up to stripe width boundaries when the current end of file is being extended and the file size is larger than the stripe width size.
wsync
When specified, all filesystem namespace operations are executed synchronously. This ensures that when the namespace operation (create, unlink, etc) completes, the change to the namespace is on stable storage. This is useful in HA setups where failover must not result in clients seeing inconsistent namespace presentation during or after a failover event.
Deprecation of V4 Format¶
The V4 filesystem format lacks certain features that are supported by the V5 format, such as metadata checksumming, strengthened metadata verification, and the ability to store timestamps past the year 2038. Because of this, the V4 format is deprecated. All users should upgrade by backing up their files, reformatting, and restoring from the backup.
Administrators and users can detect a V4 filesystem by running xfs_info against a filesystem mountpoint and checking for a string containing «crc=». If no such string is found, please upgrade xfsprogs to the latest version and try again.
The deprecation will take place in two parts. Support for mounting V4 filesystems can now be disabled at kernel build time via Kconfig option. The option will default to yes until September 2025, at which time it will be changed to default to no. In September 2030, support will be removed from the codebase entirely.
Note: Distributors may choose to withdraw V4 format support earlier than the dates listed above.