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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.
+ discard
+ Issue command 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.
+ 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
+ In memory inode hashes have been removed, so this option has
+ no function as of August 2007. Option is deprecated.
+ ikeep/noikeep
+ When ikeep is specified, XFS does not delete empty inode clusters
+ and keeps them around on disk. ikeep is the traditional XFS
+ behaviour. When noikeep is specified, empty inode clusters
+ are returned to the free space pool. The default is noikeep for
+ non-DMAPI mounts, while ikeep is the default when DMAPI is in use.
+ 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
+ the default allocation option. Applications which do not handle
+ inode numbers bigger than 32 bits, should use inode32 option.
+ inode32
+ Indicates that XFS is limited to create inodes at locations which
+ will not result in inode numbers with more than 32 bits of
+ significance. This is provided for backwards compatibility, since
+ 64 bits inode numbers might cause problems for some 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.
+ 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.
+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:
+ 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_PTAG_IFLUSH 0x00000001
+ XFS_PTAG_LOGRES 0x00000002
+ 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.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.