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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.
+
+  biosize=size
+	Sets the preferred buffered I/O size (default size is 64K).
+	"size" must be expressed as the logarithm (base2) of the
+	desired I/O size.
+	Valid values for this option are 14 through 16, inclusive
+	(i.e. 16K, 32K, and 64K bytes).  On machines with a 4K
+	pagesize, 13 (8K bytes) is also a valid size.
+	The preferred buffered I/O size can also be altered on an
+	individual file basis using the ioctl(2) system call.
+
+  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.
+
+  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 64K, 4 buffers for filesystems with a blocksize
+	of 32K, 3 buffers for filesystems with a blocksize of 16K
+	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 32MB 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.
+
+  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.
+
+  quota/usrquota/uqnoenforce
+	User disk quota accounting enabled, and limits (optionally)
+	enforced.
+
+  grpquota/gqnoenforce
+	Group disk quota accounting enabled and limits (optionally)
+	enforced.
+
+  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.
+
+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 chattr(1) 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 chattr(1) 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 chattr(1) command on a directory to be
+	inherited by files in that directory.