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 218Deprecation of V4 Format 219======================== 220 221The V4 filesystem format lacks certain features that are supported by 222the V5 format, such as metadata checksumming, strengthened metadata 223verification, and the ability to store timestamps past the year 2038. 224Because of this, the V4 format is deprecated. All users should upgrade 225by backing up their files, reformatting, and restoring from the backup. 226 227Administrators and users can detect a V4 filesystem by running xfs_info 228against a filesystem mountpoint and checking for a string containing 229"crc=". If no such string is found, please upgrade xfsprogs to the 230latest version and try again. 231 232The deprecation will take place in two parts. Support for mounting V4 233filesystems can now be disabled at kernel build time via Kconfig option. 234These options were changed to default to no in September 2025. In 235September 2030, support will be removed from the codebase entirely. 236 237Note: Distributors may choose to withdraw V4 format support earlier than 238the dates listed above. 239 240Deprecated Mount Options 241======================== 242 243============================ ================ 244 Name Removal Schedule 245============================ ================ 246Mounting with V4 filesystem September 2030 247Mounting ascii-ci filesystem September 2030 248============================ ================ 249 250 251Removed Mount Options 252===================== 253 254=========================== ======= 255 Name Removed 256=========================== ======= 257 delaylog/nodelaylog v4.0 258 ihashsize v4.0 259 irixsgid v4.0 260 osyncisdsync/osyncisosync v4.0 261 barrier v4.19 262 nobarrier v4.19 263 ikeep/noikeep v6.18 264 attr2/noattr2 v6.18 265=========================== ======= 266 267sysctls 268======= 269 270The following sysctls are available for the XFS filesystem: 271 272 fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1) 273 Setting this to "1" clears accumulated XFS statistics 274 in /proc/fs/xfs/stat. It then immediately resets to "0". 275 276 fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000) 277 The interval at which the filesystem flushes metadata 278 out to disk and runs internal cache cleanup routines. 279 280 fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000) 281 The interval at which the filesystem ages filestreams cache 282 references and returns timed-out AGs back to the free stream 283 pool. 284 285 fs.xfs.speculative_prealloc_lifetime 286 (Units: seconds Min: 1 Default: 300 Max: 86400) 287 The interval at which the background scanning for inodes 288 with unused speculative preallocation runs. The scan 289 removes unused preallocation from clean inodes and releases 290 the unused space back to the free pool. 291 292 fs.xfs.error_level (Min: 0 Default: 3 Max: 11) 293 A volume knob for error reporting when internal errors occur. 294 This will generate detailed messages & backtraces for filesystem 295 shutdowns, for example. Current threshold values are: 296 297 XFS_ERRLEVEL_OFF: 0 298 XFS_ERRLEVEL_LOW: 1 299 XFS_ERRLEVEL_HIGH: 5 300 301 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 511) 302 Causes certain error conditions to call BUG(). Value is a bitmask; 303 OR together the tags which represent errors which should cause panics: 304 305 XFS_NO_PTAG 0 306 XFS_PTAG_IFLUSH 0x00000001 307 XFS_PTAG_LOGRES 0x00000002 308 XFS_PTAG_AILDELETE 0x00000004 309 XFS_PTAG_ERROR_REPORT 0x00000008 310 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010 311 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020 312 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040 313 XFS_PTAG_FSBLOCK_ZERO 0x00000080 314 XFS_PTAG_VERIFIER_ERROR 0x00000100 315 316 This option is intended for debugging only. 317 318 fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1) 319 Setting this to "1" will cause the "sync" flag set 320 by the **xfs_io(8)** chattr command on a directory to be 321 inherited by files in that directory. 322 323 fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1) 324 Setting this to "1" will cause the "nodump" flag set 325 by the **xfs_io(8)** chattr command on a directory to be 326 inherited by files in that directory. 327 328 fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1) 329 Setting this to "1" will cause the "noatime" flag set 330 by the **xfs_io(8)** chattr command on a directory to be 331 inherited by files in that directory. 332 333 fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1) 334 Setting this to "1" will cause the "nosymlinks" flag set 335 by the **xfs_io(8)** chattr command on a directory to be 336 inherited by files in that directory. 337 338 fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1) 339 Setting this to "1" will cause the "nodefrag" flag set 340 by the **xfs_io(8)** chattr command on a directory to be 341 inherited by files in that directory. 342 343 fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256) 344 In "inode32" allocation mode, this option determines how many 345 files the allocator attempts to allocate in the same allocation 346 group before moving to the next allocation group. The intent 347 is to control the rate at which the allocator moves between 348 allocation groups when allocating extents for new files. 349 350Deprecated Sysctls 351================== 352 353None currently. 354 355Removed Sysctls 356=============== 357 358========================================== ======= 359 Name Removed 360========================================== ======= 361 fs.xfs.xfsbufd_centisec v4.0 362 fs.xfs.age_buffer_centisecs v4.0 363 fs.xfs.irix_symlink_mode v6.18 364 fs.xfs.irix_sgid_inherit v6.18 365 fs.xfs.speculative_cow_prealloc_lifetime v6.18 366========================================== ======= 367 368Error handling 369============== 370 371XFS can act differently according to the type of error found during its 372operation. The implementation introduces the following concepts to the error 373handler: 374 375 -failure speed: 376 Defines how fast XFS should propagate an error upwards when a specific 377 error is found during the filesystem operation. It can propagate 378 immediately, after a defined number of retries, after a set time period, 379 or simply retry forever. 380 381 -error classes: 382 Specifies the subsystem the error configuration will apply to, such as 383 metadata IO or memory allocation. Different subsystems will have 384 different error handlers for which behaviour can be configured. 385 386 -error handlers: 387 Defines the behavior for a specific error. 388 389The filesystem behavior during an error can be set via ``sysfs`` files. Each 390error handler works independently - the first condition met by an error handler 391for a specific class will cause the error to be propagated rather than reset and 392retried. 393 394The action taken by the filesystem when the error is propagated is context 395dependent - it may cause a shut down in the case of an unrecoverable error, 396it may be reported back to userspace, or it may even be ignored because 397there's nothing useful we can with the error or anyone we can report it to (e.g. 398during unmount). 399 400The configuration files are organized into the following hierarchy for each 401mounted filesystem: 402 403 /sys/fs/xfs/<dev>/error/<class>/<error>/ 404 405Where: 406 <dev> 407 The short device name of the mounted filesystem. This is the same device 408 name that shows up in XFS kernel error messages as "XFS(<dev>): ..." 409 410 <class> 411 The subsystem the error configuration belongs to. As of 4.9, the defined 412 classes are: 413 414 - "metadata": applies metadata buffer write IO 415 416 <error> 417 The individual error handler configurations. 418 419 420Each filesystem has "global" error configuration options defined in their top 421level directory: 422 423 /sys/fs/xfs/<dev>/error/ 424 425 fail_at_unmount (Min: 0 Default: 1 Max: 1) 426 Defines the filesystem error behavior at unmount time. 427 428 If set to a value of 1, XFS will override all other error configurations 429 during unmount and replace them with "immediate fail" characteristics. 430 i.e. no retries, no retry timeout. This will always allow unmount to 431 succeed when there are persistent errors present. 432 433 If set to 0, the configured retry behaviour will continue until all 434 retries and/or timeouts have been exhausted. This will delay unmount 435 completion when there are persistent errors, and it may prevent the 436 filesystem from ever unmounting fully in the case of "retry forever" 437 handler configurations. 438 439 Note: there is no guarantee that fail_at_unmount can be set while an 440 unmount is in progress. It is possible that the ``sysfs`` entries are 441 removed by the unmounting filesystem before a "retry forever" error 442 handler configuration causes unmount to hang, and hence the filesystem 443 must be configured appropriately before unmount begins to prevent 444 unmount hangs. 445 446Each filesystem has specific error class handlers that define the error 447propagation behaviour for specific errors. There is also a "default" error 448handler defined, which defines the behaviour for all errors that don't have 449specific handlers defined. Where multiple retry constraints are configured for 450a single error, the first retry configuration that expires will cause the error 451to be propagated. The handler configurations are found in the directory: 452 453 /sys/fs/xfs/<dev>/error/<class>/<error>/ 454 455 max_retries (Min: -1 Default: Varies Max: INTMAX) 456 Defines the allowed number of retries of a specific error before 457 the filesystem will propagate the error. The retry count for a given 458 error context (e.g. a specific metadata buffer) is reset every time 459 there is a successful completion of the operation. 460 461 Setting the value to "-1" will cause XFS to retry forever for this 462 specific error. 463 464 Setting the value to "0" will cause XFS to fail immediately when the 465 specific error is reported. 466 467 Setting the value to "N" (where 0 < N < Max) will make XFS retry the 468 operation "N" times before propagating the error. 469 470 retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day) 471 Define the amount of time (in seconds) that the filesystem is 472 allowed to retry its operations when the specific error is 473 found. 474 475 Setting the value to "-1" will allow XFS to retry forever for this 476 specific error. 477 478 Setting the value to "0" will cause XFS to fail immediately when the 479 specific error is reported. 480 481 Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the 482 operation for up to "N" seconds before propagating the error. 483 484**Note:** The default behaviour for a specific error handler is dependent on both 485the class and error context. For example, the default values for 486"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults 487to "fail immediately" behaviour. This is done because ENODEV is a fatal, 488unrecoverable error no matter how many times the metadata IO is retried. 489 490Workqueue Concurrency 491===================== 492 493XFS uses kernel workqueues to parallelize metadata update processes. This 494enables it to take advantage of storage hardware that can service many IO 495operations simultaneously. This interface exposes internal implementation 496details of XFS, and as such is explicitly not part of any userspace API/ABI 497guarantee the kernel may give userspace. These are undocumented features of 498the generic workqueue implementation XFS uses for concurrency, and they are 499provided here purely for diagnostic and tuning purposes and may change at any 500time in the future. 501 502The control knobs for a filesystem's workqueues are organized by task at hand 503and the short name of the data device. They all can be found in: 504 505 /sys/bus/workqueue/devices/${task}!${device} 506 507================ =========== 508 Task Description 509================ =========== 510 xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to 511 mount time quotacheck. 512 xfs-gc Background garbage collection of disk space that have been 513 speculatively allocated beyond EOF or for staging copy on 514 write operations. 515================ =========== 516 517For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be 518found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/. 519 520The interesting knobs for XFS workqueues are as follows: 521 522============ =========== 523 Knob Description 524============ =========== 525 max_active Maximum number of background threads that can be started to 526 run the work. 527 cpumask CPUs upon which the threads are allowed to run. 528 nice Relative priority of scheduling the threads. These are the 529 same nice levels that can be applied to userspace processes. 530============ =========== 531 532Zoned Filesystems 533================= 534 535For zoned file systems, the following attributes are exposed in: 536 537 /sys/fs/xfs/<dev>/zoned/ 538 539 max_open_zones (Min: 1 Default: Varies Max: UINTMAX) 540 This read-only attribute exposes the maximum number of open zones 541 available for data placement. The value is determined at mount time and 542 is limited by the capabilities of the backing zoned device, file system 543 size and the max_open_zones mount option. 544 545 zonegc_low_space (Min: 0 Default: 0 Max: 100) 546 Define a percentage for how much of the unused space that GC should keep 547 available for writing. A high value will reclaim more of the space 548 occupied by unused blocks, creating a larger buffer against write 549 bursts at the cost of increased write amplification. Regardless 550 of this value, garbage collection will always aim to free a minimum 551 amount of blocks to keep max_open_zones open for data placement purposes. 552