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)) interfaces.

       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.

              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

              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 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.

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