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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.
+For boolean mount options, the names with the (*) suffix is the
+default behaviour.
+
+  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.
+
+	The default behaviour 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 behaviour.
+
+  attr2
+  noattr2
+	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 behaviour is determined by the on-disk feature
+	bit indicating that attr2 behaviour 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.
+
+  barrier (*)
+  nobarrier
+	Enables/disables the use of block layer write barriers for
+	writes into the journal and for data integrity operations.
+	This allows for drive level write caching to be enabled, for
+	devices that support write barriers.
+
+  discard
+  nodiscard (*)
+	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.
+
+  grpid/bsdgroups
+  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 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.
+
+  filestreams
+	Make the data allocator use the filestreams allocation mode
+	across the entire filesystem rather than just on directories
+	configured to use it.
+
+  ikeep
+  noikeep (*)
+	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.
+
+  inode32
+  inode64 (*)
+	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.
+
+
+  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.  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 behaviour
+	is the same 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.
+
+	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.
+
+  logbsize=value
+	Set the size of each in-memory log buffer.  The 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
+	logbsize must be an integer multiple of the log
+	stripe unit configured at mkfs time.
+
+	The default value for 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.
+
+  noalign
+	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.
+
+  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,
+	and often used in combination with "norecovery" for mounting
+	read-only snapshots.
+
+  noquota
+	Forcibly turns off all quota accounting and enforcement
+	within the filesystem.
+
+  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. 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.
+
+  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.
+
+  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.
+
+
+Deprecated Mount Options
+========================
+
+None at present.
+
+
+Removed Mount Options
+=====================
+
+  Name				Removed
+  ----				-------
+  delaylog/nodelaylog		v3.20
+  ihashsize			v3.20
+  irixsgid			v3.20
+  osyncisdsync/osyncisosync	v3.20
+
+
+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 filesystem flushes metadata
+	out to disk and runs internal cache cleanup routines.
+
+  fs.xfs.filestream_centisecs	(Min: 1  Default: 3000  Max: 360000)
+	The interval at which the filesystem ages filestreams cache
+	references and returns timed-out AGs back to the free stream
+	pool.
+
+  fs.xfs.speculative_prealloc_lifetime
+		(Units: seconds   Min: 1  Default: 300  Max: 86400)
+	The interval at which the background scanning for inodes
+	with unused speculative preallocation runs. The scan
+	removes unused preallocation from clean inodes and releases
+	the unused space back to the free pool.
+
+  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: 255)
+	Causes certain error conditions to call BUG(). Value is a bitmask;
+	OR 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
+		XFS_PTAG_FSBLOCK_ZERO           0x00000080
+
+	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.inherit_nodefrag	(Min: 0  Default: 1  Max: 1)
+	Setting this to "1" will cause the "nodefrag" 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.
+
+Deprecated Sysctls
+==================
+
+None at present.
+
+
+Removed Sysctls
+===============
+
+  Name				Removed
+  ----				-------
+  fs.xfs.xfsbufd_centisec	v3.20
+  fs.xfs.age_buffer_centisecs	v3.20