1.. SPDX-License-Identifier: GPL-2.0
2
3======================
4The SGI XFS Filesystem
5======================
6
7XFS is a high performance journaling filesystem which originated
8on the SGI IRIX platform.  It is completely multi-threaded, can
9support large files and large filesystems, extended attributes,
10variable block sizes, is extent based, and makes extensive use of
11Btrees (directories, extents, free space) to aid both performance
12and scalability.
13
14Refer to the documentation at https://xfs.wiki.kernel.org/
15for further details.  This implementation is on-disk compatible
16with the IRIX version of XFS.
17
18
19Mount Options
20=============
21
22When mounting an XFS filesystem, the following options are accepted.
23
24  allocsize=size
25	Sets the buffered I/O end-of-file preallocation size when
26	doing delayed allocation writeout (default size is 64KiB).
27	Valid values for this option are page size (typically 4KiB)
28	through to 1GiB, inclusive, in power-of-2 increments.
29
30	The default behaviour is for dynamic end-of-file
31	preallocation size, which uses a set of heuristics to
32	optimise the preallocation size based on the current
33	allocation patterns within the file and the access patterns
34	to the file. Specifying a fixed ``allocsize`` value turns off
35	the dynamic behaviour.
36
37  attr2 or noattr2
38	The options enable/disable an "opportunistic" improvement to
39	be made in the way inline extended attributes are stored
40	on-disk.  When the new form is used for the first time when
41	``attr2`` is selected (either when setting or removing extended
42	attributes) the on-disk superblock feature bit field will be
43	updated to reflect this format being in use.
44
45	The default behaviour is determined by the on-disk feature
46	bit indicating that ``attr2`` behaviour is active. If either
47	mount option is set, then that becomes the new default used
48	by the filesystem.
49
50	CRC enabled filesystems always use the ``attr2`` format, and so
51	will reject the ``noattr2`` mount option if it is set.
52
53  discard or nodiscard (default)
54	Enable/disable the issuing of commands to let the block
55	device reclaim space freed by the filesystem.  This is
56	useful for SSD devices, thinly provisioned LUNs and virtual
57	machine images, but may have a performance impact.
58
59	Note: It is currently recommended that you use the ``fstrim``
60	application to ``discard`` unused blocks rather than the ``discard``
61	mount option because the performance impact of this option
62	is quite severe.
63
64  grpid/bsdgroups or nogrpid/sysvgroups (default)
65	These options define what group ID a newly created file
66	gets.  When ``grpid`` is set, it takes the group ID of the
67	directory in which it is created; otherwise it takes the
68	``fsgid`` of the current process, unless the directory has the
69	``setgid`` bit set, in which case it takes the ``gid`` from the
70	parent directory, and also gets the ``setgid`` bit set if it is
71	a directory itself.
72
73  filestreams
74	Make the data allocator use the filestreams allocation mode
75	across the entire filesystem rather than just on directories
76	configured to use it.
77
78  ikeep or noikeep (default)
79	When ``ikeep`` is specified, XFS does not delete empty inode
80	clusters and keeps them around on disk.  When ``noikeep`` is
81	specified, empty inode clusters are returned to the free
82	space pool.
83
84  inode32 or inode64 (default)
85	When ``inode32`` is specified, it indicates that XFS limits
86	inode creation to locations which will not result in inode
87	numbers with more than 32 bits of significance.
88
89	When ``inode64`` is specified, it indicates that XFS is allowed
90	to create inodes at any location in the filesystem,
91	including those which will result in inode numbers occupying
92	more than 32 bits of significance.
93
94	``inode32`` is provided for backwards compatibility with older
95	systems and applications, since 64 bits inode numbers might
96	cause problems for some applications that cannot handle
97	large inode numbers.  If applications are in use which do
98	not handle inode numbers bigger than 32 bits, the ``inode32``
99	option should be specified.
100
101  largeio or nolargeio (default)
102	If ``nolargeio`` is specified, the optimal I/O reported in
103	``st_blksize`` by **stat(2)** will be as small as possible to allow
104	user applications to avoid inefficient read/modify/write
105	I/O.  This is typically the page size of the machine, as
106	this is the granularity of the page cache.
107
108	If ``largeio`` is specified, a filesystem that was created with a
109	``swidth`` specified will return the ``swidth`` value (in bytes)
110	in ``st_blksize``. If the filesystem does not have a ``swidth``
111	specified but does specify an ``allocsize`` then ``allocsize``
112	(in bytes) will be returned instead. Otherwise the behaviour
113	is the same as if ``nolargeio`` was specified.
114
115  logbufs=value
116	Set the number of in-memory log buffers.  Valid numbers
117	range from 2-8 inclusive.
118
119	The default value is 8 buffers.
120
121	If the memory cost of 8 log buffers is too high on small
122	systems, then it may be reduced at some cost to performance
123	on metadata intensive workloads. The ``logbsize`` option below
124	controls the size of each buffer and so is also relevant to
125	this case.
126
127  logbsize=value
128	Set the size of each in-memory log buffer.  The size may be
129	specified in bytes, or in kilobytes with a "k" suffix.
130	Valid sizes for version 1 and version 2 logs are 16384 (16k)
131	and 32768 (32k).  Valid sizes for version 2 logs also
132	include 65536 (64k), 131072 (128k) and 262144 (256k). The
133	logbsize must be an integer multiple of the log
134	stripe unit configured at **mkfs(8)** time.
135
136	The default value for for version 1 logs is 32768, while the
137	default value for version 2 logs is MAX(32768, log_sunit).
138
139  logdev=device and rtdev=device
140	Use an external log (metadata journal) and/or real-time device.
141	An XFS filesystem has up to three parts: a data section, a log
142	section, and a real-time section.  The real-time section is
143	optional, and the log section can be separate from the data
144	section or contained within it.
145
146  noalign
147	Data allocations will not be aligned at stripe unit
148	boundaries. This is only relevant to filesystems created
149	with non-zero data alignment parameters (``sunit``, ``swidth``) by
150	**mkfs(8)**.
151
152  norecovery
153	The filesystem will be mounted without running log recovery.
154	If the filesystem was not cleanly unmounted, it is likely to
155	be inconsistent when mounted in ``norecovery`` mode.
156	Some files or directories may not be accessible because of this.
157	Filesystems mounted ``norecovery`` must be mounted read-only or
158	the mount will fail.
159
160  nouuid
161	Don't check for double mounted file systems using the file
162	system ``uuid``.  This is useful to mount LVM snapshot volumes,
163	and often used in combination with ``norecovery`` for mounting
164	read-only snapshots.
165
166  noquota
167	Forcibly turns off all quota accounting and enforcement
168	within the filesystem.
169
170  uquota/usrquota/uqnoenforce/quota
171	User disk quota accounting enabled, and limits (optionally)
172	enforced.  Refer to **xfs_quota(8)** for further details.
173
174  gquota/grpquota/gqnoenforce
175	Group disk quota accounting enabled and limits (optionally)
176	enforced.  Refer to **xfs_quota(8)** for further details.
177
178  pquota/prjquota/pqnoenforce
179	Project disk quota accounting enabled and limits (optionally)
180	enforced.  Refer to **xfs_quota(8)** for further details.
181
182  sunit=value and swidth=value
183	Used to specify the stripe unit and width for a RAID device
184	or a stripe volume.  "value" must be specified in 512-byte
185	block units. These options are only relevant to filesystems
186	that were created with non-zero data alignment parameters.
187
188	The ``sunit`` and ``swidth`` parameters specified must be compatible
189	with the existing filesystem alignment characteristics.  In
190	general, that means the only valid changes to ``sunit`` are
191	increasing it by a power-of-2 multiple. Valid ``swidth`` values
192	are any integer multiple of a valid ``sunit`` value.
193
194	Typically the only time these mount options are necessary if
195	after an underlying RAID device has had it's geometry
196	modified, such as adding a new disk to a RAID5 lun and
197	reshaping it.
198
199  swalloc
200	Data allocations will be rounded up to stripe width boundaries
201	when the current end of file is being extended and the file
202	size is larger than the stripe width size.
203
204  wsync
205	When specified, all filesystem namespace operations are
206	executed synchronously. This ensures that when the namespace
207	operation (create, unlink, etc) completes, the change to the
208	namespace is on stable storage. This is useful in HA setups
209	where failover must not result in clients seeing
210	inconsistent namespace presentation during or after a
211	failover event.
212
213
214Deprecated Mount Options
215========================
216
217===========================     ================
218  Name				Removal Schedule
219===========================     ================
220===========================     ================
221
222
223Removed Mount Options
224=====================
225
226===========================     =======
227  Name				Removed
228===========================	=======
229  delaylog/nodelaylog		v4.0
230  ihashsize			v4.0
231  irixsgid			v4.0
232  osyncisdsync/osyncisosync	v4.0
233  barrier			v4.19
234  nobarrier			v4.19
235===========================     =======
236
237sysctls
238=======
239
240The following sysctls are available for the XFS filesystem:
241
242  fs.xfs.stats_clear		(Min: 0  Default: 0  Max: 1)
243	Setting this to "1" clears accumulated XFS statistics
244	in /proc/fs/xfs/stat.  It then immediately resets to "0".
245
246  fs.xfs.xfssyncd_centisecs	(Min: 100  Default: 3000  Max: 720000)
247	The interval at which the filesystem flushes metadata
248	out to disk and runs internal cache cleanup routines.
249
250  fs.xfs.filestream_centisecs	(Min: 1  Default: 3000  Max: 360000)
251	The interval at which the filesystem ages filestreams cache
252	references and returns timed-out AGs back to the free stream
253	pool.
254
255  fs.xfs.speculative_prealloc_lifetime
256		(Units: seconds   Min: 1  Default: 300  Max: 86400)
257	The interval at which the background scanning for inodes
258	with unused speculative preallocation runs. The scan
259	removes unused preallocation from clean inodes and releases
260	the unused space back to the free pool.
261
262  fs.xfs.error_level		(Min: 0  Default: 3  Max: 11)
263	A volume knob for error reporting when internal errors occur.
264	This will generate detailed messages & backtraces for filesystem
265	shutdowns, for example.  Current threshold values are:
266
267		XFS_ERRLEVEL_OFF:       0
268		XFS_ERRLEVEL_LOW:       1
269		XFS_ERRLEVEL_HIGH:      5
270
271  fs.xfs.panic_mask		(Min: 0  Default: 0  Max: 256)
272	Causes certain error conditions to call BUG(). Value is a bitmask;
273	OR together the tags which represent errors which should cause panics:
274
275		XFS_NO_PTAG                     0
276		XFS_PTAG_IFLUSH                 0x00000001
277		XFS_PTAG_LOGRES                 0x00000002
278		XFS_PTAG_AILDELETE              0x00000004
279		XFS_PTAG_ERROR_REPORT           0x00000008
280		XFS_PTAG_SHUTDOWN_CORRUPT       0x00000010
281		XFS_PTAG_SHUTDOWN_IOERROR       0x00000020
282		XFS_PTAG_SHUTDOWN_LOGERROR      0x00000040
283		XFS_PTAG_FSBLOCK_ZERO           0x00000080
284		XFS_PTAG_VERIFIER_ERROR         0x00000100
285
286	This option is intended for debugging only.
287
288  fs.xfs.irix_symlink_mode	(Min: 0  Default: 0  Max: 1)
289	Controls whether symlinks are created with mode 0777 (default)
290	or whether their mode is affected by the umask (irix mode).
291
292  fs.xfs.irix_sgid_inherit	(Min: 0  Default: 0  Max: 1)
293	Controls files created in SGID directories.
294	If the group ID of the new file does not match the effective group
295	ID or one of the supplementary group IDs of the parent dir, the
296	ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl
297	is set.
298
299  fs.xfs.inherit_sync		(Min: 0  Default: 1  Max: 1)
300	Setting this to "1" will cause the "sync" flag set
301	by the **xfs_io(8)** chattr command on a directory to be
302	inherited by files in that directory.
303
304  fs.xfs.inherit_nodump		(Min: 0  Default: 1  Max: 1)
305	Setting this to "1" will cause the "nodump" flag set
306	by the **xfs_io(8)** chattr command on a directory to be
307	inherited by files in that directory.
308
309  fs.xfs.inherit_noatime	(Min: 0  Default: 1  Max: 1)
310	Setting this to "1" will cause the "noatime" flag set
311	by the **xfs_io(8)** chattr command on a directory to be
312	inherited by files in that directory.
313
314  fs.xfs.inherit_nosymlinks	(Min: 0  Default: 1  Max: 1)
315	Setting this to "1" will cause the "nosymlinks" flag set
316	by the **xfs_io(8)** chattr command on a directory to be
317	inherited by files in that directory.
318
319  fs.xfs.inherit_nodefrag	(Min: 0  Default: 1  Max: 1)
320	Setting this to "1" will cause the "nodefrag" flag set
321	by the **xfs_io(8)** chattr command on a directory to be
322	inherited by files in that directory.
323
324  fs.xfs.rotorstep		(Min: 1  Default: 1  Max: 256)
325	In "inode32" allocation mode, this option determines how many
326	files the allocator attempts to allocate in the same allocation
327	group before moving to the next allocation group.  The intent
328	is to control the rate at which the allocator moves between
329	allocation groups when allocating extents for new files.
330
331Deprecated Sysctls
332==================
333
334None at present.
335
336
337Removed Sysctls
338===============
339
340=============================	=======
341  Name				Removed
342=============================	=======
343  fs.xfs.xfsbufd_centisec	v4.0
344  fs.xfs.age_buffer_centisecs	v4.0
345=============================	=======
346
347Error handling
348==============
349
350XFS can act differently according to the type of error found during its
351operation. The implementation introduces the following concepts to the error
352handler:
353
354 -failure speed:
355	Defines how fast XFS should propagate an error upwards when a specific
356	error is found during the filesystem operation. It can propagate
357	immediately, after a defined number of retries, after a set time period,
358	or simply retry forever.
359
360 -error classes:
361	Specifies the subsystem the error configuration will apply to, such as
362	metadata IO or memory allocation. Different subsystems will have
363	different error handlers for which behaviour can be configured.
364
365 -error handlers:
366	Defines the behavior for a specific error.
367
368The filesystem behavior during an error can be set via ``sysfs`` files. Each
369error handler works independently - the first condition met by an error handler
370for a specific class will cause the error to be propagated rather than reset and
371retried.
372
373The action taken by the filesystem when the error is propagated is context
374dependent - it may cause a shut down in the case of an unrecoverable error,
375it may be reported back to userspace, or it may even be ignored because
376there's nothing useful we can with the error or anyone we can report it to (e.g.
377during unmount).
378
379The configuration files are organized into the following hierarchy for each
380mounted filesystem:
381
382  /sys/fs/xfs/<dev>/error/<class>/<error>/
383
384Where:
385  <dev>
386	The short device name of the mounted filesystem. This is the same device
387	name that shows up in XFS kernel error messages as "XFS(<dev>): ..."
388
389  <class>
390	The subsystem the error configuration belongs to. As of 4.9, the defined
391	classes are:
392
393		- "metadata": applies metadata buffer write IO
394
395  <error>
396	The individual error handler configurations.
397
398
399Each filesystem has "global" error configuration options defined in their top
400level directory:
401
402  /sys/fs/xfs/<dev>/error/
403
404  fail_at_unmount		(Min:  0  Default:  1  Max: 1)
405	Defines the filesystem error behavior at unmount time.
406
407	If set to a value of 1, XFS will override all other error configurations
408	during unmount and replace them with "immediate fail" characteristics.
409	i.e. no retries, no retry timeout. This will always allow unmount to
410	succeed when there are persistent errors present.
411
412	If set to 0, the configured retry behaviour will continue until all
413	retries and/or timeouts have been exhausted. This will delay unmount
414	completion when there are persistent errors, and it may prevent the
415	filesystem from ever unmounting fully in the case of "retry forever"
416	handler configurations.
417
418	Note: there is no guarantee that fail_at_unmount can be set while an
419	unmount is in progress. It is possible that the ``sysfs`` entries are
420	removed by the unmounting filesystem before a "retry forever" error
421	handler configuration causes unmount to hang, and hence the filesystem
422	must be configured appropriately before unmount begins to prevent
423	unmount hangs.
424
425Each filesystem has specific error class handlers that define the error
426propagation behaviour for specific errors. There is also a "default" error
427handler defined, which defines the behaviour for all errors that don't have
428specific handlers defined. Where multiple retry constraints are configured for
429a single error, the first retry configuration that expires will cause the error
430to be propagated. The handler configurations are found in the directory:
431
432  /sys/fs/xfs/<dev>/error/<class>/<error>/
433
434  max_retries			(Min: -1  Default: Varies  Max: INTMAX)
435	Defines the allowed number of retries of a specific error before
436	the filesystem will propagate the error. The retry count for a given
437	error context (e.g. a specific metadata buffer) is reset every time
438	there is a successful completion of the operation.
439
440	Setting the value to "-1" will cause XFS to retry forever for this
441	specific error.
442
443	Setting the value to "0" will cause XFS to fail immediately when the
444	specific error is reported.
445
446	Setting the value to "N" (where 0 < N < Max) will make XFS retry the
447	operation "N" times before propagating the error.
448
449  retry_timeout_seconds		(Min:  -1  Default:  Varies  Max: 1 day)
450	Define the amount of time (in seconds) that the filesystem is
451	allowed to retry its operations when the specific error is
452	found.
453
454	Setting the value to "-1" will allow XFS to retry forever for this
455	specific error.
456
457	Setting the value to "0" will cause XFS to fail immediately when the
458	specific error is reported.
459
460	Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the
461	operation for up to "N" seconds before propagating the error.
462
463**Note:** The default behaviour for a specific error handler is dependent on both
464the class and error context. For example, the default values for
465"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults
466to "fail immediately" behaviour. This is done because ENODEV is a fatal,
467unrecoverable error no matter how many times the metadata IO is retried.
468