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 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 213Deprecation of V4 Format 214======================== 215 216The V4 filesystem format lacks certain features that are supported by 217the V5 format, such as metadata checksumming, strengthened metadata 218verification, and the ability to store timestamps past the year 2038. 219Because of this, the V4 format is deprecated. All users should upgrade 220by backing up their files, reformatting, and restoring from the backup. 221 222Administrators and users can detect a V4 filesystem by running xfs_info 223against a filesystem mountpoint and checking for a string containing 224"crc=". If no such string is found, please upgrade xfsprogs to the 225latest version and try again. 226 227The deprecation will take place in two parts. Support for mounting V4 228filesystems can now be disabled at kernel build time via Kconfig option. 229The option will default to yes until September 2025, at which time it 230will be changed to default to no. In September 2030, support will be 231removed from the codebase entirely. 232 233Note: Distributors may choose to withdraw V4 format support earlier than 234the dates listed above. 235 236Deprecated Mount Options 237======================== 238 239=========================== ================ 240 Name Removal Schedule 241=========================== ================ 242Mounting with V4 filesystem September 2030 243ikeep/noikeep September 2025 244attr2/noattr2 September 2025 245=========================== ================ 246 247 248Removed Mount Options 249===================== 250 251=========================== ======= 252 Name Removed 253=========================== ======= 254 delaylog/nodelaylog v4.0 255 ihashsize v4.0 256 irixsgid v4.0 257 osyncisdsync/osyncisosync v4.0 258 barrier v4.19 259 nobarrier v4.19 260=========================== ======= 261 262sysctls 263======= 264 265The following sysctls are available for the XFS filesystem: 266 267 fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1) 268 Setting this to "1" clears accumulated XFS statistics 269 in /proc/fs/xfs/stat. It then immediately resets to "0". 270 271 fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000) 272 The interval at which the filesystem flushes metadata 273 out to disk and runs internal cache cleanup routines. 274 275 fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000) 276 The interval at which the filesystem ages filestreams cache 277 references and returns timed-out AGs back to the free stream 278 pool. 279 280 fs.xfs.speculative_prealloc_lifetime 281 (Units: seconds Min: 1 Default: 300 Max: 86400) 282 The interval at which the background scanning for inodes 283 with unused speculative preallocation runs. The scan 284 removes unused preallocation from clean inodes and releases 285 the unused space back to the free pool. 286 287 fs.xfs.speculative_cow_prealloc_lifetime 288 This is an alias for speculative_prealloc_lifetime. 289 290 fs.xfs.error_level (Min: 0 Default: 3 Max: 11) 291 A volume knob for error reporting when internal errors occur. 292 This will generate detailed messages & backtraces for filesystem 293 shutdowns, for example. Current threshold values are: 294 295 XFS_ERRLEVEL_OFF: 0 296 XFS_ERRLEVEL_LOW: 1 297 XFS_ERRLEVEL_HIGH: 5 298 299 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 256) 300 Causes certain error conditions to call BUG(). Value is a bitmask; 301 OR together the tags which represent errors which should cause panics: 302 303 XFS_NO_PTAG 0 304 XFS_PTAG_IFLUSH 0x00000001 305 XFS_PTAG_LOGRES 0x00000002 306 XFS_PTAG_AILDELETE 0x00000004 307 XFS_PTAG_ERROR_REPORT 0x00000008 308 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010 309 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020 310 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040 311 XFS_PTAG_FSBLOCK_ZERO 0x00000080 312 XFS_PTAG_VERIFIER_ERROR 0x00000100 313 314 This option is intended for debugging only. 315 316 fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1) 317 Controls whether symlinks are created with mode 0777 (default) 318 or whether their mode is affected by the umask (irix mode). 319 320 fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1) 321 Controls files created in SGID directories. 322 If the group ID of the new file does not match the effective group 323 ID or one of the supplementary group IDs of the parent dir, the 324 ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl 325 is set. 326 327 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1) 328 Setting this to "1" will cause the "sync" flag set 329 by the **xfs_io(8)** chattr command on a directory to be 330 inherited by files in that directory. 331 332 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1) 333 Setting this to "1" will cause the "nodump" flag set 334 by the **xfs_io(8)** chattr command on a directory to be 335 inherited by files in that directory. 336 337 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1) 338 Setting this to "1" will cause the "noatime" flag set 339 by the **xfs_io(8)** chattr command on a directory to be 340 inherited by files in that directory. 341 342 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1) 343 Setting this to "1" will cause the "nosymlinks" flag set 344 by the **xfs_io(8)** chattr command on a directory to be 345 inherited by files in that directory. 346 347 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1) 348 Setting this to "1" will cause the "nodefrag" flag set 349 by the **xfs_io(8)** chattr command on a directory to be 350 inherited by files in that directory. 351 352 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256) 353 In "inode32" allocation mode, this option determines how many 354 files the allocator attempts to allocate in the same allocation 355 group before moving to the next allocation group. The intent 356 is to control the rate at which the allocator moves between 357 allocation groups when allocating extents for new files. 358 359Deprecated Sysctls 360================== 361 362=========================================== ================ 363 Name Removal Schedule 364=========================================== ================ 365fs.xfs.irix_sgid_inherit September 2025 366fs.xfs.irix_symlink_mode September 2025 367fs.xfs.speculative_cow_prealloc_lifetime September 2025 368=========================================== ================ 369 370 371Removed Sysctls 372=============== 373 374============================= ======= 375 Name Removed 376============================= ======= 377 fs.xfs.xfsbufd_centisec v4.0 378 fs.xfs.age_buffer_centisecs v4.0 379============================= ======= 380 381Error handling 382============== 383 384XFS can act differently according to the type of error found during its 385operation. The implementation introduces the following concepts to the error 386handler: 387 388 -failure speed: 389 Defines how fast XFS should propagate an error upwards when a specific 390 error is found during the filesystem operation. It can propagate 391 immediately, after a defined number of retries, after a set time period, 392 or simply retry forever. 393 394 -error classes: 395 Specifies the subsystem the error configuration will apply to, such as 396 metadata IO or memory allocation. Different subsystems will have 397 different error handlers for which behaviour can be configured. 398 399 -error handlers: 400 Defines the behavior for a specific error. 401 402The filesystem behavior during an error can be set via ``sysfs`` files. Each 403error handler works independently - the first condition met by an error handler 404for a specific class will cause the error to be propagated rather than reset and 405retried. 406 407The action taken by the filesystem when the error is propagated is context 408dependent - it may cause a shut down in the case of an unrecoverable error, 409it may be reported back to userspace, or it may even be ignored because 410there's nothing useful we can with the error or anyone we can report it to (e.g. 411during unmount). 412 413The configuration files are organized into the following hierarchy for each 414mounted filesystem: 415 416 /sys/fs/xfs/<dev>/error/<class>/<error>/ 417 418Where: 419 <dev> 420 The short device name of the mounted filesystem. This is the same device 421 name that shows up in XFS kernel error messages as "XFS(<dev>): ..." 422 423 <class> 424 The subsystem the error configuration belongs to. As of 4.9, the defined 425 classes are: 426 427 - "metadata": applies metadata buffer write IO 428 429 <error> 430 The individual error handler configurations. 431 432 433Each filesystem has "global" error configuration options defined in their top 434level directory: 435 436 /sys/fs/xfs/<dev>/error/ 437 438 fail_at_unmount (Min: 0 Default: 1 Max: 1) 439 Defines the filesystem error behavior at unmount time. 440 441 If set to a value of 1, XFS will override all other error configurations 442 during unmount and replace them with "immediate fail" characteristics. 443 i.e. no retries, no retry timeout. This will always allow unmount to 444 succeed when there are persistent errors present. 445 446 If set to 0, the configured retry behaviour will continue until all 447 retries and/or timeouts have been exhausted. This will delay unmount 448 completion when there are persistent errors, and it may prevent the 449 filesystem from ever unmounting fully in the case of "retry forever" 450 handler configurations. 451 452 Note: there is no guarantee that fail_at_unmount can be set while an 453 unmount is in progress. It is possible that the ``sysfs`` entries are 454 removed by the unmounting filesystem before a "retry forever" error 455 handler configuration causes unmount to hang, and hence the filesystem 456 must be configured appropriately before unmount begins to prevent 457 unmount hangs. 458 459Each filesystem has specific error class handlers that define the error 460propagation behaviour for specific errors. There is also a "default" error 461handler defined, which defines the behaviour for all errors that don't have 462specific handlers defined. Where multiple retry constraints are configured for 463a single error, the first retry configuration that expires will cause the error 464to be propagated. The handler configurations are found in the directory: 465 466 /sys/fs/xfs/<dev>/error/<class>/<error>/ 467 468 max_retries (Min: -1 Default: Varies Max: INTMAX) 469 Defines the allowed number of retries of a specific error before 470 the filesystem will propagate the error. The retry count for a given 471 error context (e.g. a specific metadata buffer) is reset every time 472 there is a successful completion of the operation. 473 474 Setting the value to "-1" will cause XFS to retry forever for this 475 specific error. 476 477 Setting the value to "0" will cause XFS to fail immediately when the 478 specific error is reported. 479 480 Setting the value to "N" (where 0 < N < Max) will make XFS retry the 481 operation "N" times before propagating the error. 482 483 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day) 484 Define the amount of time (in seconds) that the filesystem is 485 allowed to retry its operations when the specific error is 486 found. 487 488 Setting the value to "-1" will allow XFS to retry forever for this 489 specific error. 490 491 Setting the value to "0" will cause XFS to fail immediately when the 492 specific error is reported. 493 494 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the 495 operation for up to "N" seconds before propagating the error. 496 497**Note:** The default behaviour for a specific error handler is dependent on both 498the class and error context. For example, the default values for 499"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults 500to "fail immediately" behaviour. This is done because ENODEV is a fatal, 501unrecoverable error no matter how many times the metadata IO is retried. 502 503Workqueue Concurrency 504===================== 505 506XFS uses kernel workqueues to parallelize metadata update processes. This 507enables it to take advantage of storage hardware that can service many IO 508operations simultaneously. This interface exposes internal implementation 509details of XFS, and as such is explicitly not part of any userspace API/ABI 510guarantee the kernel may give userspace. These are undocumented features of 511the generic workqueue implementation XFS uses for concurrency, and they are 512provided here purely for diagnostic and tuning purposes and may change at any 513time in the future. 514 515The control knobs for a filesystem's workqueues are organized by task at hand 516and the short name of the data device. They all can be found in: 517 518 /sys/bus/workqueue/devices/${task}!${device} 519 520================ =========== 521 Task Description 522================ =========== 523 xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to 524 mount time quotacheck. 525 xfs-gc Background garbage collection of disk space that have been 526 speculatively allocated beyond EOF or for staging copy on 527 write operations. 528================ =========== 529 530For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be 531found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/. 532 533The interesting knobs for XFS workqueues are as follows: 534 535============ =========== 536 Knob Description 537============ =========== 538 max_active Maximum number of background threads that can be started to 539 run the work. 540 cpumask CPUs upon which the threads are allowed to run. 541 nice Relative priority of scheduling the threads. These are the 542 same nice levels that can be applied to userspace processes. 543============ =========== 544