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 filesystems.

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

              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

              CRC enabled filesystems always use the attr2 format, and so
              will reject the noattr2 mount option if it is set.

              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.

              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

              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 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 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.

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
       2020-09-18.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-09-04.)  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


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