xfs(5)                         File Formats Manual                        xfs(5)

       xfs - layout, mount options, and supported file attributes for the XFS

       An XFS filesystem can reside on a regular disk partition or on a logical
       volume.  An XFS filesystem has up to three parts: a data section, a log
       section, and a realtime section.  Using the default mkfs.xfs(8) options,
       the realtime section is absent, and the log area is contained within the
       data section.  The log section can be either separate from the data
       section or contained within it.  The filesystem sections are divided into
       a certain number of blocks, whose size is specified at mkfs.xfs(8) time
       with the -b option.

       The data section contains all the filesystem metadata (inodes,
       directories, indirect blocks) as well as the user file data for ordinary
       (non-realtime) files and the log area if the log is internal to the data
       section.  The data section is divided into a number of allocation groups.
       The number and size of the allocation groups are chosen by mkfs.xfs(8) so
       that there is normally a small number of equal-sized groups.  The number
       of allocation groups controls the amount of parallelism available in file
       and block allocation.  It should be increased from the default if there
       is sufficient memory and a lot of allocation activity.  The number of
       allocation groups should not be set very high, since this can cause large
       amounts of CPU time to be used by the filesystem, especially when the
       filesystem is nearly full.  More allocation groups are added (of the
       original size) when xfs_growfs(8) is run.

       The log section (or area, if it is internal to the data section) is used
       to store changes to filesystem metadata while the filesystem is running
       until those changes are made to the data section.  It is written
       sequentially during normal operation and read only during mount.  When
       mounting a filesystem after a crash, the log is read to complete
       operations that were in progress at the time of the crash.

       The realtime section is used to store the data of realtime files.  These
       files had an attribute bit set through xfsctl(3) after file creation,
       before any data was written to the file.  The realtime section is divided
       into a number of extents of fixed size (specified at mkfs.xfs(8) time).
       Each file in the realtime section has an extent size that is a multiple
       of the realtime section extent size.

       Each allocation group contains several data structures.  The first sector
       contains the superblock.  For allocation groups after the first, the
       superblock is just a copy and is not updated after mkfs.xfs(8).  The next
       three sectors contain information for block and inode allocation within
       the allocation group.  Also contained within each allocation group are
       data structures to locate free blocks and inodes; these are located
       through the header structures.

       Each XFS filesystem is labeled with a Universal Unique Identifier (UUID).
       The UUID is stored in every allocation group header and is used to help
       distinguish one XFS filesystem from another, therefore you should avoid
       using dd(1) or other block-by-block copying programs to copy XFS
       filesystems.  If two XFS filesystems on the same machine have the same
       UUID, xfsdump(8) may become confused when doing incremental and resumed
       dumps.  xfsdump(8) and xfsrestore(8) are recommended for making copies of
       XFS filesystems.

       Some functionality specific to the XFS filesystem is accessible to
       applications through the xfsctl(3) and by-handle (see open_by_handle(3))

       The following XFS-specific mount options may be used when mounting an XFS
       filesystem. Other generic options may be used as well; refer to the
       mount(8) manual page for more details.

              Sets the buffered I/O end-of-file preallocation size when doing
              delayed allocation writeout. Valid values for this option are page
              size (typically 4KiB) through to 1GiB, inclusive, in power-of-2

              The default behavior 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 behavior.

              Note: These options have been deprecated as of kernel v5.10; The
              noattr2 option will be removed no earlier than in September 2025
              and attr2 option will be immutable default.

              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 behavior is determined by the on-disk feature bit
              indicating that attr2 behavior is active. If either mount option
              it 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.

              Set CPU direct access (DAX) behavior for the current filesystem.
              This mount option accepts the following values:

              "dax=inode" DAX will be enabled only on regular files with
              FS_XFLAG_DAX applied.

              "dax=never" DAX will not be enabled for any files. FS_XFLAG_DAX
              will be ignored.

              "dax=always" DAX will be enabled for all regular files, regardless
              of the FS_XFLAG_DAX state.

              If no option is used when mounting a filesystem stored on a DAX
              capable device, dax=inode will be used as default.

              For details regarding DAX behavior in kernel, please refer to
              kernel's documentation at filesystems/dax.txt

              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.  For this reason, nodiscard is the 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.

              Make the data allocator use the filestreams allocation mode across
              the entire filesystem rather than just on directories configured
              to use it.

              Note: These options have been deprecated as of kernel v5.10; The
              noikeep option will be removed no earlier than in September 2025
              and ikeep option will be immutable 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.  noikeep is
              the 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

              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.

              For kernel v3.7 and later, inode64 is the 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" 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 behavior is the same as if
              "nolargeio" was specified.  nolargeio is the default.

              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.

              Set the size of each in-memory log buffer.  The size may be
              specified in bytes, or in kibibytes (KiB) with a "k" suffix.
              Valid sizes for version 1 and version 2 logs are 16384 (value=16k)
              and 32768 (value=32k).  Valid sizes for version 2 logs also
              include 65536 (value=64k), 131072 (value=128k) and 262144
              (value=256k). The logbsize must be an integer multiple of the log
              stripe unit configured at mkfs 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.

              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.

              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

       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

              Forcibly turns off all quota accounting and enforcement within the

              User disk quota accounting enabled, and limits (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

              Group disk quota accounting enabled and limits (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

              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.

              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.

       The following mount options have been removed from the kernel, and will
       yield mount failures if specified.  Mount options are deprecated for a
       significant period time prior to removal.

       Name                        Removed
       ----                        -------
       delaylog/nodelaylog         v4.0
       ihashsize                   v4.0
       irixsgid                    v4.0
       osyncisdsync/osyncisosync   v4.0
       barrier/nobarrier           v4.19

       The XFS filesystem supports setting the following file attributes on
       Linux systems using the chattr(1) utility:

       a - append only

       A - no atime updates

       d - no dump

       i - immutable

       S - synchronous updates

       For descriptions of these attribute flags, please refer to the chattr(1)
       man page.

       chattr(1), xfsctl(3), mount(8), mkfs.xfs(8), xfs_info(8), xfs_admin(8),
       xfsdump(8), xfsrestore(8).