xfs(5) — Linux manual page


xfs(5)                     File Formats Manual                    xfs(5)

NAME         top

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

DESCRIPTION         top

       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

OPERATIONS         top

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

MOUNT OPTIONS         top

       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 increments.

              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

              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

              "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

              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 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.

              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

              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.

              Forcibly turns off all quota accounting and enforcement
              within the filesystem.

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

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

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

       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

              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.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the xfsprogs (utilities for XFS filesystems)
       project.  Information about the project can be found at 
       ⟨http://xfs.org/⟩.  If you have a bug report for this manual page,
       send it to linux-xfs@vger.kernel.org.  This page was obtained
       from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git⟩ on
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-17.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org


Pages that refer to this page: chattr(1)FS_IOC_SETFLAGS(2const)mount_setattr(2)handle(3)xfsctl(3)filesystems(5)dmstats(8)fsck.xfs(8)mount(8)systemd-makefs@.service(8)xfs_admin(8)xfs_bmap(8)xfs_copy(8)xfs_db(8)xfsdump(8)xfs_freeze(8)xfs_fsr(8)xfs_growfs(8)xfs_io(8)xfs_logprint(8)xfs_mdrestore(8)xfs_metadump(8)xfs_ncheck(8)xfs_quota(8)xfs_repair(8)xfs_rtcp(8)