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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 http://oss.sgi.com/projects/xfs/
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.

  attr2/noattr2
        The options enable/disable (default is disabled for backward
        compatibility on-disk) 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 (by setting or
        removing extended attributes) the on-disk superblock feature
        bit field will be updated to reflect this format being in use.

  barrier
        Enables the use of block layer write barriers for writes into
        the journal and unwritten extent conversion.  This allows for
        drive level write caching to be enabled, for devices that
        support write barriers.

  dmapi
        Enable the DMAPI (Data Management API) event callouts.
        Use with the "mtpt" option.

  grpid/bsdgroups and nogrpid/sysvgroups
        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 (the default) 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.

  ihashsize=value
        Sets the number of hash buckets available for hashing the
        in-memory inodes of the specified mount point.  If a value
        of zero is used, the value selected by the default algorithm
        will be displayed in /proc/mounts.

  ikeep/noikeep
        When inode clusters are emptied of inodes, keep them around
        on the disk (ikeep) - this is the traditional XFS behaviour
        and is still the default for now.  Using the noikeep option,
        inode clusters are returned to the free space pool.

  inode64
        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.  This is
        provided for backwards compatibility, but causes problems for
        backup applications that cannot handle large inode numbers.

  largeio/nolargeio
        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.
        If "largeio" specified, a filesystem that has 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.
        If neither of these two options are specified, then filesystem
        will behave 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 for filesystems with a
        blocksize of 64KiB, 4 buffers for filesystems with a blocksize
        of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB
        and 2 buffers for all other configurations.  Increasing the
        number of buffers may increase performance on some workloads
        at the cost of the memory used for the additional log buffers
        and their associated control structures.

  logbsize=value
        Set the size of each in-memory log buffer.
        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 default value for machines with more than 32MiB of memory
        is 32768, machines with less memory use 16384 by default.

  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.

  mtpt=mountpoint
        Use with the "dmapi" option.  The value specified here will be
        included in the DMAPI mount event, and should be the path of
        the actual mountpoint that is used.

  noalign
        Data allocations will not be aligned at stripe unit boundaries.

  noatime
        Access timestamps are not updated when a file is read.

  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.

  osyncisosync
        Make O_SYNC writes implement true O_SYNC.  WITHOUT this option,
        Linux XFS behaves as if an "osyncisdsync" option is used,
        which will make writes to files opened with the O_SYNC flag set
        behave as if the O_DSYNC flag had been used instead.
        This can result in better performance without compromising
        data safety.
        However if this option is not in effect, timestamp updates from
        O_SYNC writes can be lost if the system crashes.
        If timestamp updates are critical, use the osyncisosync option.

  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.
        If this option is not specified and the filesystem was made on
        a stripe volume or the stripe width or unit were specified for
        the RAID device at mkfs time, then the mount system call will
        restore the value from the superblock.  For filesystems that
        are made directly on RAID devices, these options can be used
        to override the information in the superblock if the underlying
        disk layout changes after the filesystem has been created.
        The "swidth" option is required if the "sunit" option has been
        specified, and must be a multiple of the "sunit" value.

  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.


sysctls
=======

The following sysctls are available for the XFS filesystem:

  fs.xfs.stats_clear            (Min: 0  Default: 0  Max: 1)
        Setting this to "1" clears accumulated XFS statistics
        in /proc/fs/xfs/stat.  It then immediately resets to "0".

  fs.xfs.xfssyncd_centisecs     (Min: 100  Default: 3000  Max: 720000)
        The interval at which the xfssyncd thread flushes metadata
        out to disk.  This thread will flush log activity out, and
        do some processing on unlinked inodes.

  fs.xfs.xfsbufd_centisecs      (Min: 50  Default: 100  Max: 3000)
        The interval at which xfsbufd scans the dirty metadata buffers list.

  fs.xfs.age_buffer_centisecs   (Min: 100  Default: 1500  Max: 720000)
        The age at which xfsbufd flushes dirty metadata buffers to disk.

  fs.xfs.error_level            (Min: 0  Default: 3  Max: 11)
        A volume knob for error reporting when internal errors occur.
        This will generate detailed messages & backtraces for filesystem
        shutdowns, for example.  Current threshold values are:

                XFS_ERRLEVEL_OFF:       0
                XFS_ERRLEVEL_LOW:       1
                XFS_ERRLEVEL_HIGH:      5

  fs.xfs.panic_mask             (Min: 0  Default: 0  Max: 127)
        Causes certain error conditions to call BUG(). Value is a bitmask;
        AND together the tags which represent errors which should cause panics:

                XFS_NO_PTAG                     0
                XFS_PTAG_IFLUSH                 0x00000001
                XFS_PTAG_LOGRES                 0x00000002
                XFS_PTAG_AILDELETE              0x00000004
                XFS_PTAG_ERROR_REPORT           0x00000008
                XFS_PTAG_SHUTDOWN_CORRUPT       0x00000010
                XFS_PTAG_SHUTDOWN_IOERROR       0x00000020
                XFS_PTAG_SHUTDOWN_LOGERROR      0x00000040

        This option is intended for debugging only.

  fs.xfs.irix_symlink_mode      (Min: 0  Default: 0  Max: 1)
        Controls whether symlinks are created with mode 0777 (default)
        or whether their mode is affected by the umask (irix mode).

  fs.xfs.irix_sgid_inherit      (Min: 0  Default: 0  Max: 1)
        Controls files created in SGID directories.
        If the group ID of the new file does not match the effective group
        ID or one of the supplementary group IDs of the parent dir, the
        ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl
        is set.

  fs.xfs.restrict_chown         (Min: 0  Default: 1  Max: 1)
        Controls whether unprivileged users can use chown to "give away"
        a file to another user.

  fs.xfs.inherit_sync           (Min: 0  Default: 1  Max: 1)
        Setting this to "1" will cause the "sync" flag set
        by the xfs_io(8) chattr command on a directory to be
        inherited by files in that directory.

  fs.xfs.inherit_nodump         (Min: 0  Default: 1  Max: 1)
        Setting this to "1" will cause the "nodump" flag set
        by the xfs_io(8) chattr command on a directory to be
        inherited by files in that directory.

  fs.xfs.inherit_noatime        (Min: 0  Default: 1  Max: 1)
        Setting this to "1" will cause the "noatime" flag set
        by the xfs_io(8) chattr command on a directory to be
        inherited by files in that directory.

  fs.xfs.inherit_nosymlinks     (Min: 0  Default: 1  Max: 1)
        Setting this to "1" will cause the "nosymlinks" flag set
        by the xfs_io(8) chattr command on a directory to be
        inherited by files in that directory.

  fs.xfs.rotorstep              (Min: 1  Default: 1  Max: 256)
        In "inode32" allocation mode, this option determines how many
        files the allocator attempts to allocate in the same allocation
        group before moving to the next allocation group.  The intent
        is to control the rate at which the allocator moves between
        allocation groups when allocating extents for new files.