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1.. SPDX-License-Identifier: GPL-2.02 3======================4The SGI XFS Filesystem5======================6 7XFS is a high performance journaling filesystem which originated8on the SGI IRIX platform. It is completely multi-threaded, can9support large files and large filesystems, extended attributes,10variable block sizes, is extent based, and makes extensive use of11Btrees (directories, extents, free space) to aid both performance12and scalability.13 14Refer to the documentation at https://xfs.wiki.kernel.org/15for further details. This implementation is on-disk compatible16with the IRIX version of XFS.17 18 19Mount Options20=============21 22When mounting an XFS filesystem, the following options are accepted.23 24 allocsize=size25 Sets the buffered I/O end-of-file preallocation size when26 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-file31 preallocation size, which uses a set of heuristics to32 optimise the preallocation size based on the current33 allocation patterns within the file and the access patterns34 to the file. Specifying a fixed ``allocsize`` value turns off35 the dynamic behaviour.36 37 attr2 or noattr238 The options enable/disable an "opportunistic" improvement to39 be made in the way inline extended attributes are stored40 on-disk. When the new form is used for the first time when41 ``attr2`` is selected (either when setting or removing extended42 attributes) the on-disk superblock feature bit field will be43 updated to reflect this format being in use.44 45 The default behaviour is determined by the on-disk feature46 bit indicating that ``attr2`` behaviour is active. If either47 mount option is set, then that becomes the new default used48 by the filesystem.49 50 CRC enabled filesystems always use the ``attr2`` format, and so51 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 block55 device reclaim space freed by the filesystem. This is56 useful for SSD devices, thinly provisioned LUNs and virtual57 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 option62 is quite severe.63 64 grpid/bsdgroups or nogrpid/sysvgroups (default)65 These options define what group ID a newly created file66 gets. When ``grpid`` is set, it takes the group ID of the67 directory in which it is created; otherwise it takes the68 ``fsgid`` of the current process, unless the directory has the69 ``setgid`` bit set, in which case it takes the ``gid`` from the70 parent directory, and also gets the ``setgid`` bit set if it is71 a directory itself.72 73 filestreams74 Make the data allocator use the filestreams allocation mode75 across the entire filesystem rather than just on directories76 configured to use it.77 78 ikeep or noikeep (default)79 When ``ikeep`` is specified, XFS does not delete empty inode80 clusters and keeps them around on disk. When ``noikeep`` is81 specified, empty inode clusters are returned to the free82 space pool.83 84 inode32 or inode64 (default)85 When ``inode32`` is specified, it indicates that XFS limits86 inode creation to locations which will not result in inode87 numbers with more than 32 bits of significance.88 89 When ``inode64`` is specified, it indicates that XFS is allowed90 to create inodes at any location in the filesystem,91 including those which will result in inode numbers occupying92 more than 32 bits of significance.93 94 ``inode32`` is provided for backwards compatibility with older95 systems and applications, since 64 bits inode numbers might96 cause problems for some applications that cannot handle97 large inode numbers. If applications are in use which do98 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 in103 ``st_blksize`` by **stat(2)** will be as small as possible to allow104 user applications to avoid inefficient read/modify/write105 I/O. This is typically the page size of the machine, as106 this is the granularity of the page cache.107 108 If ``largeio`` is specified, a filesystem that was created with a109 ``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 behaviour113 is the same as if ``nolargeio`` was specified.114 115 logbufs=value116 Set the number of in-memory log buffers. Valid numbers117 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 small122 systems, then it may be reduced at some cost to performance123 on metadata intensive workloads. The ``logbsize`` option below124 controls the size of each buffer and so is also relevant to125 this case.126 127 logbsize=value128 Set the size of each in-memory log buffer. The size may be129 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 also132 include 65536 (64k), 131072 (128k) and 262144 (256k). The133 logbsize must be an integer multiple of the log134 stripe unit configured at **mkfs(8)** time.135 136 The default value for version 1 logs is 32768, while the137 default value for version 2 logs is MAX(32768, log_sunit).138 139 logdev=device and rtdev=device140 Use an external log (metadata journal) and/or real-time device.141 An XFS filesystem has up to three parts: a data section, a log142 section, and a real-time section. The real-time section is143 optional, and the log section can be separate from the data144 section or contained within it.145 146 noalign147 Data allocations will not be aligned at stripe unit148 boundaries. This is only relevant to filesystems created149 with non-zero data alignment parameters (``sunit``, ``swidth``) by150 **mkfs(8)**.151 152 norecovery153 The filesystem will be mounted without running log recovery.154 If the filesystem was not cleanly unmounted, it is likely to155 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 or158 the mount will fail.159 160 nouuid161 Don't check for double mounted file systems using the file162 system ``uuid``. This is useful to mount LVM snapshot volumes,163 and often used in combination with ``norecovery`` for mounting164 read-only snapshots.165 166 noquota167 Forcibly turns off all quota accounting and enforcement168 within the filesystem.169 170 uquota/usrquota/uqnoenforce/quota171 User disk quota accounting enabled, and limits (optionally)172 enforced. Refer to **xfs_quota(8)** for further details.173 174 gquota/grpquota/gqnoenforce175 Group disk quota accounting enabled and limits (optionally)176 enforced. Refer to **xfs_quota(8)** for further details.177 178 pquota/prjquota/pqnoenforce179 Project disk quota accounting enabled and limits (optionally)180 enforced. Refer to **xfs_quota(8)** for further details.181 182 sunit=value and swidth=value183 Used to specify the stripe unit and width for a RAID device184 or a stripe volume. "value" must be specified in 512-byte185 block units. These options are only relevant to filesystems186 that were created with non-zero data alignment parameters.187 188 The ``sunit`` and ``swidth`` parameters specified must be compatible189 with the existing filesystem alignment characteristics. In190 general, that means the only valid changes to ``sunit`` are191 increasing it by a power-of-2 multiple. Valid ``swidth`` values192 are any integer multiple of a valid ``sunit`` value.193 194 Typically the only time these mount options are necessary if195 after an underlying RAID device has had its geometry196 modified, such as adding a new disk to a RAID5 lun and197 reshaping it.198 199 swalloc200 Data allocations will be rounded up to stripe width boundaries201 when the current end of file is being extended and the file202 size is larger than the stripe width size.203 204 wsync205 When specified, all filesystem namespace operations are206 executed synchronously. This ensures that when the namespace207 operation (create, unlink, etc) completes, the change to the208 namespace is on stable storage. This is useful in HA setups209 where failover must not result in clients seeing210 inconsistent namespace presentation during or after a211 failover event.212 213Deprecation of V4 Format214========================215 216The V4 filesystem format lacks certain features that are supported by217the V5 format, such as metadata checksumming, strengthened metadata218verification, and the ability to store timestamps past the year 2038.219Because of this, the V4 format is deprecated. All users should upgrade220by backing up their files, reformatting, and restoring from the backup.221 222Administrators and users can detect a V4 filesystem by running xfs_info223against a filesystem mountpoint and checking for a string containing224"crc=". If no such string is found, please upgrade xfsprogs to the225latest version and try again.226 227The deprecation will take place in two parts. Support for mounting V4228filesystems can now be disabled at kernel build time via Kconfig option.229The option will default to yes until September 2025, at which time it230will be changed to default to no. In September 2030, support will be231removed from the codebase entirely.232 233Note: Distributors may choose to withdraw V4 format support earlier than234the dates listed above.235 236Deprecated Mount Options237========================238 239============================ ================240 Name Removal Schedule241============================ ================242Mounting with V4 filesystem September 2030243Mounting ascii-ci filesystem September 2030244ikeep/noikeep September 2025245attr2/noattr2 September 2025246============================ ================247 248 249Removed Mount Options250=====================251 252=========================== =======253 Name Removed254=========================== =======255 delaylog/nodelaylog v4.0256 ihashsize v4.0257 irixsgid v4.0258 osyncisdsync/osyncisosync v4.0259 barrier v4.19260 nobarrier v4.19261=========================== =======262 263sysctls264=======265 266The following sysctls are available for the XFS filesystem:267 268 fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1)269 Setting this to "1" clears accumulated XFS statistics270 in /proc/fs/xfs/stat. It then immediately resets to "0".271 272 fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000)273 The interval at which the filesystem flushes metadata274 out to disk and runs internal cache cleanup routines.275 276 fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000)277 The interval at which the filesystem ages filestreams cache278 references and returns timed-out AGs back to the free stream279 pool.280 281 fs.xfs.speculative_prealloc_lifetime282 (Units: seconds Min: 1 Default: 300 Max: 86400)283 The interval at which the background scanning for inodes284 with unused speculative preallocation runs. The scan285 removes unused preallocation from clean inodes and releases286 the unused space back to the free pool.287 288 fs.xfs.speculative_cow_prealloc_lifetime289 This is an alias for speculative_prealloc_lifetime.290 291 fs.xfs.error_level (Min: 0 Default: 3 Max: 11)292 A volume knob for error reporting when internal errors occur.293 This will generate detailed messages & backtraces for filesystem294 shutdowns, for example. Current threshold values are:295 296 XFS_ERRLEVEL_OFF: 0297 XFS_ERRLEVEL_LOW: 1298 XFS_ERRLEVEL_HIGH: 5299 300 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 511)301 Causes certain error conditions to call BUG(). Value is a bitmask;302 OR together the tags which represent errors which should cause panics:303 304 XFS_NO_PTAG 0305 XFS_PTAG_IFLUSH 0x00000001306 XFS_PTAG_LOGRES 0x00000002307 XFS_PTAG_AILDELETE 0x00000004308 XFS_PTAG_ERROR_REPORT 0x00000008309 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010310 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020311 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040312 XFS_PTAG_FSBLOCK_ZERO 0x00000080313 XFS_PTAG_VERIFIER_ERROR 0x00000100314 315 This option is intended for debugging only.316 317 fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1)318 Controls whether symlinks are created with mode 0777 (default)319 or whether their mode is affected by the umask (irix mode).320 321 fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1)322 Controls files created in SGID directories.323 If the group ID of the new file does not match the effective group324 ID or one of the supplementary group IDs of the parent dir, the325 ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl326 is set.327 328 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1)329 Setting this to "1" will cause the "sync" flag set330 by the **xfs_io(8)** chattr command on a directory to be331 inherited by files in that directory.332 333 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1)334 Setting this to "1" will cause the "nodump" flag set335 by the **xfs_io(8)** chattr command on a directory to be336 inherited by files in that directory.337 338 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1)339 Setting this to "1" will cause the "noatime" flag set340 by the **xfs_io(8)** chattr command on a directory to be341 inherited by files in that directory.342 343 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1)344 Setting this to "1" will cause the "nosymlinks" flag set345 by the **xfs_io(8)** chattr command on a directory to be346 inherited by files in that directory.347 348 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1)349 Setting this to "1" will cause the "nodefrag" flag set350 by the **xfs_io(8)** chattr command on a directory to be351 inherited by files in that directory.352 353 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256)354 In "inode32" allocation mode, this option determines how many355 files the allocator attempts to allocate in the same allocation356 group before moving to the next allocation group. The intent357 is to control the rate at which the allocator moves between358 allocation groups when allocating extents for new files.359 360Deprecated Sysctls361==================362 363=========================================== ================364 Name Removal Schedule365=========================================== ================366fs.xfs.irix_sgid_inherit September 2025367fs.xfs.irix_symlink_mode September 2025368fs.xfs.speculative_cow_prealloc_lifetime September 2025369=========================================== ================370 371 372Removed Sysctls373===============374 375============================= =======376 Name Removed377============================= =======378 fs.xfs.xfsbufd_centisec v4.0379 fs.xfs.age_buffer_centisecs v4.0380============================= =======381 382Error handling383==============384 385XFS can act differently according to the type of error found during its386operation. The implementation introduces the following concepts to the error387handler:388 389 -failure speed:390 Defines how fast XFS should propagate an error upwards when a specific391 error is found during the filesystem operation. It can propagate392 immediately, after a defined number of retries, after a set time period,393 or simply retry forever.394 395 -error classes:396 Specifies the subsystem the error configuration will apply to, such as397 metadata IO or memory allocation. Different subsystems will have398 different error handlers for which behaviour can be configured.399 400 -error handlers:401 Defines the behavior for a specific error.402 403The filesystem behavior during an error can be set via ``sysfs`` files. Each404error handler works independently - the first condition met by an error handler405for a specific class will cause the error to be propagated rather than reset and406retried.407 408The action taken by the filesystem when the error is propagated is context409dependent - it may cause a shut down in the case of an unrecoverable error,410it may be reported back to userspace, or it may even be ignored because411there's nothing useful we can with the error or anyone we can report it to (e.g.412during unmount).413 414The configuration files are organized into the following hierarchy for each415mounted filesystem:416 417 /sys/fs/xfs/<dev>/error/<class>/<error>/418 419Where:420 <dev>421 The short device name of the mounted filesystem. This is the same device422 name that shows up in XFS kernel error messages as "XFS(<dev>): ..."423 424 <class>425 The subsystem the error configuration belongs to. As of 4.9, the defined426 classes are:427 428 - "metadata": applies metadata buffer write IO429 430 <error>431 The individual error handler configurations.432 433 434Each filesystem has "global" error configuration options defined in their top435level directory:436 437 /sys/fs/xfs/<dev>/error/438 439 fail_at_unmount (Min: 0 Default: 1 Max: 1)440 Defines the filesystem error behavior at unmount time.441 442 If set to a value of 1, XFS will override all other error configurations443 during unmount and replace them with "immediate fail" characteristics.444 i.e. no retries, no retry timeout. This will always allow unmount to445 succeed when there are persistent errors present.446 447 If set to 0, the configured retry behaviour will continue until all448 retries and/or timeouts have been exhausted. This will delay unmount449 completion when there are persistent errors, and it may prevent the450 filesystem from ever unmounting fully in the case of "retry forever"451 handler configurations.452 453 Note: there is no guarantee that fail_at_unmount can be set while an454 unmount is in progress. It is possible that the ``sysfs`` entries are455 removed by the unmounting filesystem before a "retry forever" error456 handler configuration causes unmount to hang, and hence the filesystem457 must be configured appropriately before unmount begins to prevent458 unmount hangs.459 460Each filesystem has specific error class handlers that define the error461propagation behaviour for specific errors. There is also a "default" error462handler defined, which defines the behaviour for all errors that don't have463specific handlers defined. Where multiple retry constraints are configured for464a single error, the first retry configuration that expires will cause the error465to be propagated. The handler configurations are found in the directory:466 467 /sys/fs/xfs/<dev>/error/<class>/<error>/468 469 max_retries (Min: -1 Default: Varies Max: INTMAX)470 Defines the allowed number of retries of a specific error before471 the filesystem will propagate the error. The retry count for a given472 error context (e.g. a specific metadata buffer) is reset every time473 there is a successful completion of the operation.474 475 Setting the value to "-1" will cause XFS to retry forever for this476 specific error.477 478 Setting the value to "0" will cause XFS to fail immediately when the479 specific error is reported.480 481 Setting the value to "N" (where 0 < N < Max) will make XFS retry the482 operation "N" times before propagating the error.483 484 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day)485 Define the amount of time (in seconds) that the filesystem is486 allowed to retry its operations when the specific error is487 found.488 489 Setting the value to "-1" will allow XFS to retry forever for this490 specific error.491 492 Setting the value to "0" will cause XFS to fail immediately when the493 specific error is reported.494 495 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the496 operation for up to "N" seconds before propagating the error.497 498**Note:** The default behaviour for a specific error handler is dependent on both499the class and error context. For example, the default values for500"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults501to "fail immediately" behaviour. This is done because ENODEV is a fatal,502unrecoverable error no matter how many times the metadata IO is retried.503 504Workqueue Concurrency505=====================506 507XFS uses kernel workqueues to parallelize metadata update processes. This508enables it to take advantage of storage hardware that can service many IO509operations simultaneously. This interface exposes internal implementation510details of XFS, and as such is explicitly not part of any userspace API/ABI511guarantee the kernel may give userspace. These are undocumented features of512the generic workqueue implementation XFS uses for concurrency, and they are513provided here purely for diagnostic and tuning purposes and may change at any514time in the future.515 516The control knobs for a filesystem's workqueues are organized by task at hand517and the short name of the data device. They all can be found in:518 519 /sys/bus/workqueue/devices/${task}!${device}520 521================ ===========522 Task Description523================ ===========524 xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to525 mount time quotacheck.526 xfs-gc Background garbage collection of disk space that have been527 speculatively allocated beyond EOF or for staging copy on528 write operations.529================ ===========530 531For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be532found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/.533 534The interesting knobs for XFS workqueues are as follows:535 536============ ===========537 Knob Description538============ ===========539 max_active Maximum number of background threads that can be started to540 run the work.541 cpumask CPUs upon which the threads are allowed to run.542 nice Relative priority of scheduling the threads. These are the543 same nice levels that can be applied to userspace processes.544============ ===========545