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.error_level (Min: 0 Default: 3 Max: 11) 288 A volume knob for error reporting when internal errors occur. 289 This will generate detailed messages & backtraces for filesystem 290 shutdowns, for example. Current threshold values are: 291 292 XFS_ERRLEVEL_OFF: 0 293 XFS_ERRLEVEL_LOW: 1 294 XFS_ERRLEVEL_HIGH: 5 295 296 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 256) 297 Causes certain error conditions to call BUG(). Value is a bitmask; 298 OR together the tags which represent errors which should cause panics: 299 300 XFS_NO_PTAG 0 301 XFS_PTAG_IFLUSH 0x00000001 302 XFS_PTAG_LOGRES 0x00000002 303 XFS_PTAG_AILDELETE 0x00000004 304 XFS_PTAG_ERROR_REPORT 0x00000008 305 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010 306 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020 307 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040 308 XFS_PTAG_FSBLOCK_ZERO 0x00000080 309 XFS_PTAG_VERIFIER_ERROR 0x00000100 310 311 This option is intended for debugging only. 312 313 fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1) 314 Controls whether symlinks are created with mode 0777 (default) 315 or whether their mode is affected by the umask (irix mode). 316 317 fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1) 318 Controls files created in SGID directories. 319 If the group ID of the new file does not match the effective group 320 ID or one of the supplementary group IDs of the parent dir, the 321 ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl 322 is set. 323 324 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1) 325 Setting this to "1" will cause the "sync" flag set 326 by the **xfs_io(8)** chattr command on a directory to be 327 inherited by files in that directory. 328 329 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1) 330 Setting this to "1" will cause the "nodump" flag set 331 by the **xfs_io(8)** chattr command on a directory to be 332 inherited by files in that directory. 333 334 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1) 335 Setting this to "1" will cause the "noatime" flag set 336 by the **xfs_io(8)** chattr command on a directory to be 337 inherited by files in that directory. 338 339 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1) 340 Setting this to "1" will cause the "nosymlinks" flag set 341 by the **xfs_io(8)** chattr command on a directory to be 342 inherited by files in that directory. 343 344 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1) 345 Setting this to "1" will cause the "nodefrag" flag set 346 by the **xfs_io(8)** chattr command on a directory to be 347 inherited by files in that directory. 348 349 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256) 350 In "inode32" allocation mode, this option determines how many 351 files the allocator attempts to allocate in the same allocation 352 group before moving to the next allocation group. The intent 353 is to control the rate at which the allocator moves between 354 allocation groups when allocating extents for new files. 355 356Deprecated Sysctls 357================== 358 359=========================== ================ 360 Name Removal Schedule 361=========================== ================ 362fs.xfs.irix_sgid_inherit September 2025 363fs.xfs.irix_symlink_mode September 2025 364=========================== ================ 365 366 367Removed Sysctls 368=============== 369 370============================= ======= 371 Name Removed 372============================= ======= 373 fs.xfs.xfsbufd_centisec v4.0 374 fs.xfs.age_buffer_centisecs v4.0 375============================= ======= 376 377Error handling 378============== 379 380XFS can act differently according to the type of error found during its 381operation. The implementation introduces the following concepts to the error 382handler: 383 384 -failure speed: 385 Defines how fast XFS should propagate an error upwards when a specific 386 error is found during the filesystem operation. It can propagate 387 immediately, after a defined number of retries, after a set time period, 388 or simply retry forever. 389 390 -error classes: 391 Specifies the subsystem the error configuration will apply to, such as 392 metadata IO or memory allocation. Different subsystems will have 393 different error handlers for which behaviour can be configured. 394 395 -error handlers: 396 Defines the behavior for a specific error. 397 398The filesystem behavior during an error can be set via ``sysfs`` files. Each 399error handler works independently - the first condition met by an error handler 400for a specific class will cause the error to be propagated rather than reset and 401retried. 402 403The action taken by the filesystem when the error is propagated is context 404dependent - it may cause a shut down in the case of an unrecoverable error, 405it may be reported back to userspace, or it may even be ignored because 406there's nothing useful we can with the error or anyone we can report it to (e.g. 407during unmount). 408 409The configuration files are organized into the following hierarchy for each 410mounted filesystem: 411 412 /sys/fs/xfs/<dev>/error/<class>/<error>/ 413 414Where: 415 <dev> 416 The short device name of the mounted filesystem. This is the same device 417 name that shows up in XFS kernel error messages as "XFS(<dev>): ..." 418 419 <class> 420 The subsystem the error configuration belongs to. As of 4.9, the defined 421 classes are: 422 423 - "metadata": applies metadata buffer write IO 424 425 <error> 426 The individual error handler configurations. 427 428 429Each filesystem has "global" error configuration options defined in their top 430level directory: 431 432 /sys/fs/xfs/<dev>/error/ 433 434 fail_at_unmount (Min: 0 Default: 1 Max: 1) 435 Defines the filesystem error behavior at unmount time. 436 437 If set to a value of 1, XFS will override all other error configurations 438 during unmount and replace them with "immediate fail" characteristics. 439 i.e. no retries, no retry timeout. This will always allow unmount to 440 succeed when there are persistent errors present. 441 442 If set to 0, the configured retry behaviour will continue until all 443 retries and/or timeouts have been exhausted. This will delay unmount 444 completion when there are persistent errors, and it may prevent the 445 filesystem from ever unmounting fully in the case of "retry forever" 446 handler configurations. 447 448 Note: there is no guarantee that fail_at_unmount can be set while an 449 unmount is in progress. It is possible that the ``sysfs`` entries are 450 removed by the unmounting filesystem before a "retry forever" error 451 handler configuration causes unmount to hang, and hence the filesystem 452 must be configured appropriately before unmount begins to prevent 453 unmount hangs. 454 455Each filesystem has specific error class handlers that define the error 456propagation behaviour for specific errors. There is also a "default" error 457handler defined, which defines the behaviour for all errors that don't have 458specific handlers defined. Where multiple retry constraints are configured for 459a single error, the first retry configuration that expires will cause the error 460to be propagated. The handler configurations are found in the directory: 461 462 /sys/fs/xfs/<dev>/error/<class>/<error>/ 463 464 max_retries (Min: -1 Default: Varies Max: INTMAX) 465 Defines the allowed number of retries of a specific error before 466 the filesystem will propagate the error. The retry count for a given 467 error context (e.g. a specific metadata buffer) is reset every time 468 there is a successful completion of the operation. 469 470 Setting the value to "-1" will cause XFS to retry forever for this 471 specific error. 472 473 Setting the value to "0" will cause XFS to fail immediately when the 474 specific error is reported. 475 476 Setting the value to "N" (where 0 < N < Max) will make XFS retry the 477 operation "N" times before propagating the error. 478 479 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day) 480 Define the amount of time (in seconds) that the filesystem is 481 allowed to retry its operations when the specific error is 482 found. 483 484 Setting the value to "-1" will allow XFS to retry forever for this 485 specific error. 486 487 Setting the value to "0" will cause XFS to fail immediately when the 488 specific error is reported. 489 490 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the 491 operation for up to "N" seconds before propagating the error. 492 493**Note:** The default behaviour for a specific error handler is dependent on both 494the class and error context. For example, the default values for 495"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults 496to "fail immediately" behaviour. This is done because ENODEV is a fatal, 497unrecoverable error no matter how many times the metadata IO is retried. 498