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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 discard or nodiscard (default)
38 Enable/disable the issuing of commands to let the block
39 device reclaim space freed by the filesystem. This is
40 useful for SSD devices, thinly provisioned LUNs and virtual
41 machine images, but may have a performance impact.
42
43 Note: It is currently recommended that you use the ``fstrim``
44 application to ``discard`` unused blocks rather than the ``discard``
45 mount option because the performance impact of this option
46 is quite severe.
47
48 grpid/bsdgroups or nogrpid/sysvgroups (default)
49 These options define what group ID a newly created file
50 gets. When ``grpid`` is set, it takes the group ID of the
51 directory in which it is created; otherwise it takes the
52 ``fsgid`` of the current process, unless the directory has the
53 ``setgid`` bit set, in which case it takes the ``gid`` from the
54 parent directory, and also gets the ``setgid`` bit set if it is
55 a directory itself.
56
57 filestreams
58 Make the data allocator use the filestreams allocation mode
59 across the entire filesystem rather than just on directories
60 configured to use it.
61
62 inode32 or inode64 (default)
63 When ``inode32`` is specified, it indicates that XFS limits
64 inode creation to locations which will not result in inode
65 numbers with more than 32 bits of significance.
66
67 When ``inode64`` is specified, it indicates that XFS is allowed
68 to create inodes at any location in the filesystem,
69 including those which will result in inode numbers occupying
70 more than 32 bits of significance.
71
72 ``inode32`` is provided for backwards compatibility with older
73 systems and applications, since 64 bits inode numbers might
74 cause problems for some applications that cannot handle
75 large inode numbers. If applications are in use which do
76 not handle inode numbers bigger than 32 bits, the ``inode32``
77 option should be specified.
78
79 largeio or nolargeio (default)
80 If ``nolargeio`` is specified, the optimal I/O reported in
81 ``st_blksize`` by **stat(2)** will be as small as possible to allow
82 user applications to avoid inefficient read/modify/write
83 I/O. This is typically the page size of the machine, as
84 this is the granularity of the page cache.
85
86 If ``largeio`` is specified, a filesystem that was created with a
87 ``swidth`` specified will return the ``swidth`` value (in bytes)
88 in ``st_blksize``. If the filesystem does not have a ``swidth``
89 specified but does specify an ``allocsize`` then ``allocsize``
90 (in bytes) will be returned instead. Otherwise the behaviour
91 is the same as if ``nolargeio`` was specified.
92
93 logbufs=value
94 Set the number of in-memory log buffers. Valid numbers
95 range from 2-8 inclusive.
96
97 The default value is 8 buffers.
98
99 If the memory cost of 8 log buffers is too high on small
100 systems, then it may be reduced at some cost to performance
101 on metadata intensive workloads. The ``logbsize`` option below
102 controls the size of each buffer and so is also relevant to
103 this case.
104
105 lifetime (default) or nolifetime
106 Enable data placement based on write life time hints provided
107 by the user. This turns on co-allocation of data of similar
108 life times when statistically favorable to reduce garbage
109 collection cost.
110
111 These options are only available for zoned rt file systems.
112
113 logbsize=value
114 Set the size of each in-memory log buffer. The size may be
115 specified in bytes, or in kilobytes with a "k" suffix.
116 Valid sizes for version 1 and version 2 logs are 16384 (16k)
117 and 32768 (32k). Valid sizes for version 2 logs also
118 include 65536 (64k), 131072 (128k) and 262144 (256k). The
119 logbsize must be an integer multiple of the log
120 stripe unit configured at **mkfs(8)** time.
121
122 The default value for version 1 logs is 32768, while the
123 default value for version 2 logs is MAX(32768, log_sunit).
124
125 logdev=device and rtdev=device
126 Use an external log (metadata journal) and/or real-time device.
127 An XFS filesystem has up to three parts: a data section, a log
128 section, and a real-time section. The real-time section is
129 optional, and the log section can be separate from the data
130 section or contained within it.
131
132 max_atomic_write=value
133 Set the maximum size of an atomic write. The size may be
134 specified in bytes, in kilobytes with a "k" suffix, in megabytes
135 with a "m" suffix, or in gigabytes with a "g" suffix. The size
136 cannot be larger than the maximum write size, larger than the
137 size of any allocation group, or larger than the size of a
138 remapping operation that the log can complete atomically.
139
140 The default value is to set the maximum I/O completion size
141 to allow each CPU to handle one at a time.
142
143 max_open_zones=value
144 Specify the max number of zones to keep open for writing on a
145 zoned rt device. Many open zones aids file data separation
146 but may impact performance on HDDs.
147
148 If ``max_open_zones`` is not specified, the value is determined
149 by the capabilities and the size of the zoned rt device.
150
151 noalign
152 Data allocations will not be aligned at stripe unit
153 boundaries. This is only relevant to filesystems created
154 with non-zero data alignment parameters (``sunit``, ``swidth``) by
155 **mkfs(8)**.
156
157 norecovery
158 The filesystem will be mounted without running log recovery.
159 If the filesystem was not cleanly unmounted, it is likely to
160 be inconsistent when mounted in ``norecovery`` mode.
161 Some files or directories may not be accessible because of this.
162 Filesystems mounted ``norecovery`` must be mounted read-only or
163 the mount will fail.
164
165 nouuid
166 Don't check for double mounted file systems using the file
167 system ``uuid``. This is useful to mount LVM snapshot volumes,
168 and often used in combination with ``norecovery`` for mounting
169 read-only snapshots.
170
171 noquota
172 Forcibly turns off all quota accounting and enforcement
173 within the filesystem.
174
175 uquota/usrquota/uqnoenforce/quota
176 User disk quota accounting enabled, and limits (optionally)
177 enforced. Refer to **xfs_quota(8)** for further details.
178
179 gquota/grpquota/gqnoenforce
180 Group disk quota accounting enabled and limits (optionally)
181 enforced. Refer to **xfs_quota(8)** for further details.
182
183 pquota/prjquota/pqnoenforce
184 Project disk quota accounting enabled and limits (optionally)
185 enforced. Refer to **xfs_quota(8)** for further details.
186
187 sunit=value and swidth=value
188 Used to specify the stripe unit and width for a RAID device
189 or a stripe volume. "value" must be specified in 512-byte
190 block units. These options are only relevant to filesystems
191 that were created with non-zero data alignment parameters.
192
193 The ``sunit`` and ``swidth`` parameters specified must be compatible
194 with the existing filesystem alignment characteristics. In
195 general, that means the only valid changes to ``sunit`` are
196 increasing it by a power-of-2 multiple. Valid ``swidth`` values
197 are any integer multiple of a valid ``sunit`` value.
198
199 Typically the only time these mount options are necessary if
200 after an underlying RAID device has had its geometry
201 modified, such as adding a new disk to a RAID5 lun and
202 reshaping it.
203
204 swalloc
205 Data allocations will be rounded up to stripe width boundaries
206 when the current end of file is being extended and the file
207 size is larger than the stripe width size.
208
209 wsync
210 When specified, all filesystem namespace operations are
211 executed synchronously. This ensures that when the namespace
212 operation (create, unlink, etc) completes, the change to the
213 namespace is on stable storage. This is useful in HA setups
214 where failover must not result in clients seeing
215 inconsistent namespace presentation during or after a
216 failover event.
217
218 errortag=tagname
219 When specified, enables the error inject tag named "tagname" with the
220 default frequency. Can be specified multiple times to enable multiple
221 errortags. Specifying this option on remount will reset the error tag
222 to the default value if it was set to any other value before.
223 This option is only supported when CONFIG_XFS_DEBUG is enabled, and
224 will not be reflected in /proc/self/mounts.
225
226Deprecation of V4 Format
227========================
228
229The V4 filesystem format lacks certain features that are supported by
230the V5 format, such as metadata checksumming, strengthened metadata
231verification, and the ability to store timestamps past the year 2038.
232Because of this, the V4 format is deprecated. All users should upgrade
233by backing up their files, reformatting, and restoring from the backup.
234
235Administrators and users can detect a V4 filesystem by running xfs_info
236against a filesystem mountpoint and checking for a string containing
237"crc=". If no such string is found, please upgrade xfsprogs to the
238latest version and try again.
239
240The deprecation will take place in two parts. Support for mounting V4
241filesystems can now be disabled at kernel build time via Kconfig option.
242These options were changed to default to no in September 2025. In
243September 2030, support will be removed from the codebase entirely.
244
245Note: Distributors may choose to withdraw V4 format support earlier than
246the dates listed above.
247
248Deprecated Mount Options
249========================
250
251============================ ================
252 Name Removal Schedule
253============================ ================
254Mounting with V4 filesystem September 2030
255Mounting ascii-ci filesystem September 2030
256============================ ================
257
258
259Removed Mount Options
260=====================
261
262=========================== =======
263 Name Removed
264=========================== =======
265 delaylog/nodelaylog v4.0
266 ihashsize v4.0
267 irixsgid v4.0
268 osyncisdsync/osyncisosync v4.0
269 barrier v4.19
270 nobarrier v4.19
271 ikeep/noikeep v6.18
272 attr2/noattr2 v6.18
273=========================== =======
274
275sysctls
276=======
277
278The following sysctls are available for the XFS filesystem:
279
280 fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1)
281 Setting this to "1" clears accumulated XFS statistics
282 in /proc/fs/xfs/stat. It then immediately resets to "0".
283
284 fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000)
285 The interval at which the filesystem flushes metadata
286 out to disk and runs internal cache cleanup routines.
287
288 fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000)
289 The interval at which the filesystem ages filestreams cache
290 references and returns timed-out AGs back to the free stream
291 pool.
292
293 fs.xfs.speculative_prealloc_lifetime
294 (Units: seconds Min: 1 Default: 300 Max: 86400)
295 The interval at which the background scanning for inodes
296 with unused speculative preallocation runs. The scan
297 removes unused preallocation from clean inodes and releases
298 the unused space back to the free pool.
299
300 fs.xfs.error_level (Min: 0 Default: 3 Max: 11)
301 A volume knob for error reporting when internal errors occur.
302 This will generate detailed messages & backtraces for filesystem
303 shutdowns, for example. Current threshold values are:
304
305 XFS_ERRLEVEL_OFF: 0
306 XFS_ERRLEVEL_LOW: 1
307 XFS_ERRLEVEL_HIGH: 5
308
309 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 511)
310 Causes certain error conditions to call BUG(). Value is a bitmask;
311 OR together the tags which represent errors which should cause panics:
312
313 XFS_NO_PTAG 0
314 XFS_PTAG_IFLUSH 0x00000001
315 XFS_PTAG_LOGRES 0x00000002
316 XFS_PTAG_AILDELETE 0x00000004
317 XFS_PTAG_ERROR_REPORT 0x00000008
318 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010
319 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020
320 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040
321 XFS_PTAG_FSBLOCK_ZERO 0x00000080
322 XFS_PTAG_VERIFIER_ERROR 0x00000100
323
324 This option is intended for debugging only.
325
326 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1)
327 Setting this to "1" will cause the "sync" flag set
328 by the **xfs_io(8)** chattr command on a directory to be
329 inherited by files in that directory.
330
331 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1)
332 Setting this to "1" will cause the "nodump" flag set
333 by the **xfs_io(8)** chattr command on a directory to be
334 inherited by files in that directory.
335
336 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1)
337 Setting this to "1" will cause the "noatime" flag set
338 by the **xfs_io(8)** chattr command on a directory to be
339 inherited by files in that directory.
340
341 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1)
342 Setting this to "1" will cause the "nosymlinks" flag set
343 by the **xfs_io(8)** chattr command on a directory to be
344 inherited by files in that directory.
345
346 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1)
347 Setting this to "1" will cause the "nodefrag" flag set
348 by the **xfs_io(8)** chattr command on a directory to be
349 inherited by files in that directory.
350
351 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256)
352 In "inode32" allocation mode, this option determines how many
353 files the allocator attempts to allocate in the same allocation
354 group before moving to the next allocation group. The intent
355 is to control the rate at which the allocator moves between
356 allocation groups when allocating extents for new files.
357
358Deprecated Sysctls
359==================
360
361None currently.
362
363Removed Sysctls
364===============
365
366========================================== =======
367 Name Removed
368========================================== =======
369 fs.xfs.xfsbufd_centisec v4.0
370 fs.xfs.age_buffer_centisecs v4.0
371 fs.xfs.irix_symlink_mode v6.18
372 fs.xfs.irix_sgid_inherit v6.18
373 fs.xfs.speculative_cow_prealloc_lifetime v6.18
374========================================== =======
375
376Error handling
377==============
378
379XFS can act differently according to the type of error found during its
380operation. The implementation introduces the following concepts to the error
381handler:
382
383 -failure speed:
384 Defines how fast XFS should propagate an error upwards when a specific
385 error is found during the filesystem operation. It can propagate
386 immediately, after a defined number of retries, after a set time period,
387 or simply retry forever.
388
389 -error classes:
390 Specifies the subsystem the error configuration will apply to, such as
391 metadata IO or memory allocation. Different subsystems will have
392 different error handlers for which behaviour can be configured.
393
394 -error handlers:
395 Defines the behavior for a specific error.
396
397The filesystem behavior during an error can be set via ``sysfs`` files. Each
398error handler works independently - the first condition met by an error handler
399for a specific class will cause the error to be propagated rather than reset and
400retried.
401
402The action taken by the filesystem when the error is propagated is context
403dependent - it may cause a shut down in the case of an unrecoverable error,
404it may be reported back to userspace, or it may even be ignored because
405there's nothing useful we can with the error or anyone we can report it to (e.g.
406during unmount).
407
408The configuration files are organized into the following hierarchy for each
409mounted filesystem:
410
411 /sys/fs/xfs/<dev>/error/<class>/<error>/
412
413Where:
414 <dev>
415 The short device name of the mounted filesystem. This is the same device
416 name that shows up in XFS kernel error messages as "XFS(<dev>): ..."
417
418 <class>
419 The subsystem the error configuration belongs to. As of 4.9, the defined
420 classes are:
421
422 - "metadata": applies metadata buffer write IO
423
424 <error>
425 The individual error handler configurations.
426
427
428Each filesystem has "global" error configuration options defined in their top
429level directory:
430
431 /sys/fs/xfs/<dev>/error/
432
433 fail_at_unmount (Min: 0 Default: 1 Max: 1)
434 Defines the filesystem error behavior at unmount time.
435
436 If set to a value of 1, XFS will override all other error configurations
437 during unmount and replace them with "immediate fail" characteristics.
438 i.e. no retries, no retry timeout. This will always allow unmount to
439 succeed when there are persistent errors present.
440
441 If set to 0, the configured retry behaviour will continue until all
442 retries and/or timeouts have been exhausted. This will delay unmount
443 completion when there are persistent errors, and it may prevent the
444 filesystem from ever unmounting fully in the case of "retry forever"
445 handler configurations.
446
447 Note: there is no guarantee that fail_at_unmount can be set while an
448 unmount is in progress. It is possible that the ``sysfs`` entries are
449 removed by the unmounting filesystem before a "retry forever" error
450 handler configuration causes unmount to hang, and hence the filesystem
451 must be configured appropriately before unmount begins to prevent
452 unmount hangs.
453
454Each filesystem has specific error class handlers that define the error
455propagation behaviour for specific errors. There is also a "default" error
456handler defined, which defines the behaviour for all errors that don't have
457specific handlers defined. Where multiple retry constraints are configured for
458a single error, the first retry configuration that expires will cause the error
459to be propagated. The handler configurations are found in the directory:
460
461 /sys/fs/xfs/<dev>/error/<class>/<error>/
462
463 max_retries (Min: -1 Default: Varies Max: INTMAX)
464 Defines the allowed number of retries of a specific error before
465 the filesystem will propagate the error. The retry count for a given
466 error context (e.g. a specific metadata buffer) is reset every time
467 there is a successful completion of the operation.
468
469 Setting the value to "-1" will cause XFS to retry forever for this
470 specific error.
471
472 Setting the value to "0" will cause XFS to fail immediately when the
473 specific error is reported.
474
475 Setting the value to "N" (where 0 < N < Max) will make XFS retry the
476 operation "N" times before propagating the error.
477
478 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day)
479 Define the amount of time (in seconds) that the filesystem is
480 allowed to retry its operations when the specific error is
481 found.
482
483 Setting the value to "-1" will allow XFS to retry forever for this
484 specific error.
485
486 Setting the value to "0" will cause XFS to fail immediately when the
487 specific error is reported.
488
489 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the
490 operation for up to "N" seconds before propagating the error.
491
492**Note:** The default behaviour for a specific error handler is dependent on both
493the class and error context. For example, the default values for
494"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults
495to "fail immediately" behaviour. This is done because ENODEV is a fatal,
496unrecoverable error no matter how many times the metadata IO is retried.
497
498Workqueue Concurrency
499=====================
500
501XFS uses kernel workqueues to parallelize metadata update processes. This
502enables it to take advantage of storage hardware that can service many IO
503operations simultaneously. This interface exposes internal implementation
504details of XFS, and as such is explicitly not part of any userspace API/ABI
505guarantee the kernel may give userspace. These are undocumented features of
506the generic workqueue implementation XFS uses for concurrency, and they are
507provided here purely for diagnostic and tuning purposes and may change at any
508time in the future.
509
510The control knobs for a filesystem's workqueues are organized by task at hand
511and the short name of the data device. They all can be found in:
512
513 /sys/bus/workqueue/devices/${task}!${device}
514
515================ ===========
516 Task Description
517================ ===========
518 xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to
519 mount time quotacheck.
520 xfs-gc Background garbage collection of disk space that have been
521 speculatively allocated beyond EOF or for staging copy on
522 write operations.
523================ ===========
524
525For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be
526found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/.
527
528The interesting knobs for XFS workqueues are as follows:
529
530============ ===========
531 Knob Description
532============ ===========
533 max_active Maximum number of background threads that can be started to
534 run the work.
535 cpumask CPUs upon which the threads are allowed to run.
536 nice Relative priority of scheduling the threads. These are the
537 same nice levels that can be applied to userspace processes.
538============ ===========
539
540Zoned Filesystems
541=================
542
543For zoned file systems, the following attributes are exposed in:
544
545 /sys/fs/xfs/<dev>/zoned/
546
547 max_open_zones (Min: 1 Default: Varies Max: UINTMAX)
548 This read-only attribute exposes the maximum number of open zones
549 available for data placement. The value is determined at mount time and
550 is limited by the capabilities of the backing zoned device, file system
551 size and the max_open_zones mount option.
552
553 nr_open_zones (Min: 0 Default: Varies Max: UINTMAX)
554 This read-only attribute exposes the current number of open zones
555 used by the file system.
556
557 zonegc_low_space (Min: 0 Default: 0 Max: 100)
558 Define a percentage for how much of the unused space that GC should keep
559 available for writing. A high value will reclaim more of the space
560 occupied by unused blocks, creating a larger buffer against write
561 bursts at the cost of increased write amplification. Regardless
562 of this value, garbage collection will always aim to free a minimum
563 amount of blocks to keep max_open_zones open for data placement purposes.