The SGI XFS Filesystem

요약·해설과 원문, 전문 번역을 서로 분리했습니다. API 이름, symbol, source path는 원문 표기를 사용합니다.

1. 요약·해설

원문의 핵심 논리와 kernel programming 관점의 보충 설명입니다. 아래의 전문 번역과는 별도로 작성했습니다.

요약과 해설

xfs.rst:1-551

XFS는 extent와 Btree를 기반으로 큰 file·filesystem을 확장성 있게 처리합니다. 운영 시에는 mount option의 정렬·quota·journal·recovery 의미와, sysfs error handler의 retry 종료 조건을 정확히 구분해야 합니다.

운영 영역	핵심 주의점
Mount	`discard`보다 `fstrim` 권장, `norecovery`는 read-only 필수
Format	V4는 deprecated이며 2030년 9월 제거 예정
Error	여러 retry 조건 중 먼저 만료된 조건이 error를 전달
Workqueue	내부 tuning interface로 API/ABI 보장 없음
Zoned	open zone 한도와 GC 여유 공간의 trade-off 관리

2. 영어 원문 전체

번역 기준이 된 Linux v6.18.37 원문입니다. 줄 번호는 이 버전의 파일 좌표입니다.

원문 전체 펼치기

1 .. SPDX-License-Identifier: GPL-2.0

3 ======================

4 The SGI XFS Filesystem

5 ======================

7 XFS is a high performance journaling filesystem which originated

8 on the SGI IRIX platform. It is completely multi-threaded, can

9 support large files and large filesystems, extended attributes,

10 variable block sizes, is extent based, and makes extensive use of

11 Btrees (directories, extents, free space) to aid both performance

12 and scalability.

14 Refer to the documentation at https://xfs.wiki.kernel.org/

15 for further details. This implementation is on-disk compatible

16 with the IRIX version of XFS.

19 Mount Options

20 =============

22 When mounting an XFS filesystem, the following options are accepted.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

93 logbufs=value

94 Set the number of in-memory log buffers. Valid numbers

95 range from 2-8 inclusive.

97 The default value is 8 buffers.

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 Deprecation of V4 Format

219 ========================

220

221 The V4 filesystem format lacks certain features that are supported by

222 the V5 format, such as metadata checksumming, strengthened metadata

223 verification, and the ability to store timestamps past the year 2038.

224 Because of this, the V4 format is deprecated. All users should upgrade

225 by backing up their files, reformatting, and restoring from the backup.

226

227 Administrators and users can detect a V4 filesystem by running xfs_info

228 against a filesystem mountpoint and checking for a string containing

229 "crc=". If no such string is found, please upgrade xfsprogs to the

230 latest version and try again.

231

232 The deprecation will take place in two parts. Support for mounting V4

233 filesystems can now be disabled at kernel build time via Kconfig option.

234 These options were changed to default to no in September 2025. In

235 September 2030, support will be removed from the codebase entirely.

236

237 Note: Distributors may choose to withdraw V4 format support earlier than

238 the dates listed above.

239

240 Deprecated Mount Options

241 ========================

242

243 ============================ ================

244 Name Removal Schedule

245 ============================ ================

246 Mounting with V4 filesystem September 2030

247 Mounting ascii-ci filesystem September 2030

248 ============================ ================

249

250

251 Removed 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

267 sysctls

268 =======

269

270 The 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

350 Deprecated Sysctls

351 ==================

352

353 None currently.

354

355 Removed 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

368 Error handling

369 ==============

370

371 XFS can act differently according to the type of error found during its

372 operation. The implementation introduces the following concepts to the error

373 handler:

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

389 The filesystem behavior during an error can be set via ``sysfs`` files. Each

390 error handler works independently - the first condition met by an error handler

391 for a specific class will cause the error to be propagated rather than reset and

392 retried.

393

394 The action taken by the filesystem when the error is propagated is context

395 dependent - it may cause a shut down in the case of an unrecoverable error,

396 it may be reported back to userspace, or it may even be ignored because

397 there's nothing useful we can with the error or anyone we can report it to (e.g.

398 during unmount).

399

400 The configuration files are organized into the following hierarchy for each

401 mounted filesystem:

402

403 /sys/fs/xfs/<dev>/error/<class>/<error>/

404

405 Where:

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

420 Each filesystem has "global" error configuration options defined in their top

421 level 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

446 Each filesystem has specific error class handlers that define the error

447 propagation behaviour for specific errors. There is also a "default" error

448 handler defined, which defines the behaviour for all errors that don't have

449 specific handlers defined. Where multiple retry constraints are configured for

450 a single error, the first retry configuration that expires will cause the error

451 to 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

485 the class and error context. For example, the default values for

486 "metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults

487 to "fail immediately" behaviour. This is done because ENODEV is a fatal,

488 unrecoverable error no matter how many times the metadata IO is retried.

489

490 Workqueue Concurrency

491 =====================

492

493 XFS uses kernel workqueues to parallelize metadata update processes. This

494 enables it to take advantage of storage hardware that can service many IO

495 operations simultaneously. This interface exposes internal implementation

496 details of XFS, and as such is explicitly not part of any userspace API/ABI

497 guarantee the kernel may give userspace. These are undocumented features of

498 the generic workqueue implementation XFS uses for concurrency, and they are

499 provided here purely for diagnostic and tuning purposes and may change at any

500 time in the future.

501

502 The control knobs for a filesystem's workqueues are organized by task at hand

503 and 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

517 For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be

518 found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/.

519

520 The 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

532 Zoned Filesystems

533 =================

534

535 For 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

3. 한국어 전문 번역

영어 원문의 문단 순서와 의미를 유지한 전체 번역입니다. 코드, 함수명, symbol과 URL은 원문 표기를 유지합니다.

1-18

XFS는 SGI IRIX에서 시작한 고성능 journaling filesystem입니다. 완전한 multi-thread 구조이며 큰 file과 filesystem, extended attribute, 가변 block size를 지원합니다. extent 기반이고 directory, extent, free space에 Btree를 폭넓게 사용해 성능과 확장성을 높입니다.

자세한 내용은 `https://xfs.wiki.kernel.org/`에서 볼 수 있습니다. Linux 구현의 on-disk 형식은 IRIX XFS와 호환됩니다. 라이선스는 `GPL-2.0`입니다.

Mount Options

19-217

XFS filesystem을 mount할 때 다음 option을 사용할 수 있습니다.

option	동작과 제약
`allocsize=size`	delayed allocation writeout 때 buffered I/O EOF preallocation 크기를 고정합니다. 기본은 64KiB이며 page size(보통 4KiB)부터 1GiB까지 2의 거듭제곱 단위가 유효합니다. 기본 dynamic heuristic은 allocation·access pattern으로 크기를 최적화하지만 고정 `allocsize`를 지정하면 꺼집니다.
`discard` / `nodiscard`(기본)	filesystem이 해제한 공간을 block device가 회수하도록 할지 정합니다. SSD, thin-provisioned LUN, VM image에 유용하지만 성능 영향이 큽니다. mount `discard`보다 `fstrim` application 사용을 권장합니다.
`grpid`/`bsdgroups` / `nogrpid`/`sysvgroups`(기본)	`grpid`이면 새 file은 parent directory의 group ID를 받습니다. 아니면 현재 process의 `fsgid`를 쓰되 parent에 `setgid`가 있으면 parent `gid`를 받고, 새 directory에도 `setgid`가 설정됩니다.
`filestreams`	filestreams를 지정한 directory뿐 아니라 filesystem 전체에서 data allocator의 filestreams allocation mode를 사용합니다.
`inode32` / `inode64`(기본)	`inode32`는 32bit보다 큰 inode number가 생기지 않는 위치로 inode 생성을 제한합니다. `inode64`는 filesystem 어디든 허용합니다. 큰 inode number를 처리하지 못하는 구형 system·application 호환이 필요할 때만 `inode32`를 사용합니다.
`largeio` / `nolargeio`(기본)	`nolargeio`는 stat(2)의 `st_blksize`를 보통 page size로 작게 보고해 비효율적인 read/modify/write를 피하게 합니다. `largeio`는 mkfs의 `swidth`, 없으면 `allocsize`를 byte 단위로 보고하며 둘 다 없으면 `nolargeio`와 같습니다.
`logbufs=value`	memory log buffer 수를 2~8로 설정하며 기본은 8입니다. 작은 system에서 memory 비용을 줄일 수 있지만 metadata 집중 workload 성능이 떨어질 수 있고, 각 buffer 크기는 `logbsize`가 정합니다.
`lifetime`(기본) / `nolifetime`	user가 준 write lifetime hint를 바탕으로 비슷한 수명의 data를 통계적으로 유리할 때 함께 배치해 garbage collection 비용을 줄입니다. zoned rt filesystem에서만 사용할 수 있습니다.
`logbsize=value`	memory log buffer 하나의 크기입니다. byte 또는 `k` suffix를 씁니다. v1·v2 log는 16k와 32k, v2는 64k·128k·256k도 허용합니다. mkfs(8)의 log stripe unit 정수배여야 하며 기본은 v1 32768, v2 `MAX(32768, log_sunit)`입니다.
`logdev=device` / `rtdev=device`	외부 metadata journal과 real-time device를 사용합니다. XFS는 data, log, 선택적 real-time의 최대 세 부분으로 구성되고 log는 data 안에 있거나 별도일 수 있습니다.
`max_atomic_write=value`	atomic write 최대 크기를 byte 또는 `k`, `m`, `g` suffix로 정합니다. 최대 write 크기, allocation group 크기, log가 atomically 완료할 remap 크기를 넘을 수 없습니다. 기본은 CPU마다 I/O completion 하나를 처리할 수 있게 정합니다.
`max_open_zones=value`	zoned rt device에서 write용으로 열어 둘 zone 최대 수입니다. zone을 많이 열면 file data 분리에 도움이 되지만 HDD 성능에 영향을 줄 수 있습니다. 생략하면 device capability와 rt device 크기로 결정합니다.
`noalign`	data allocation을 stripe unit 경계에 맞추지 않습니다. mkfs(8)에서 `sunit`, `swidth` 같은 non-zero data alignment로 만든 filesystem에만 의미가 있습니다.
`norecovery`	log recovery 없이 mount합니다. clean unmount가 아니면 inconsistent할 가능성이 있고 file·directory에 접근하지 못할 수 있습니다. 반드시 read-only로 mount해야 합니다.
`nouuid`	filesystem `uuid`를 이용한 double-mount 검사를 하지 않습니다. LVM snapshot volume에 유용하며 read-only snapshot에는 `norecovery`와 자주 함께 씁니다.
`noquota`	filesystem의 모든 quota accounting과 enforcement를 강제로 끕니다.
`uquota`/`usrquota`/`uqnoenforce`/`quota`	user disk quota accounting을 켜고 선택적으로 limit을 강제합니다. 자세한 내용은 xfs_quota(8)를 참조합니다.
`gquota`/`grpquota`/`gqnoenforce`	group disk quota accounting을 켜고 선택적으로 limit을 강제합니다.
`pquota`/`prjquota`/`pqnoenforce`	project disk quota accounting을 켜고 선택적으로 limit을 강제합니다.
`sunit=value` / `swidth=value`	RAID device나 stripe volume의 stripe unit·width를 512-byte block 단위로 지정합니다. 기존 alignment와 호환되어야 하며 `sunit`은 보통 2의 거듭제곱 배로만 늘릴 수 있고 `swidth`는 유효한 `sunit`의 정수배여야 합니다. RAID geometry를 바꾼 뒤 주로 필요합니다.
`swalloc`	EOF를 늘릴 때 file 크기가 stripe width보다 크면 data allocation을 stripe width 경계까지 올림합니다.
`wsync`	create, unlink 같은 filesystem namespace operation을 모두 동기 실행해 완료 시 stable storage에 반영되게 합니다. failover 중·후 client가 inconsistent namespace를 보면 안 되는 HA setup에 유용합니다.

Deprecation of V4 Format

218-239

V4 filesystem format에는 V5가 지원하는 metadata checksum, 강화된 metadata verification, 2038년 이후 timestamp 저장 기능이 없습니다. 따라서 V4는 deprecated이며 file을 backup하고 V5로 다시 format한 뒤 restore해야 합니다.

`xfs_info`를 mountpoint에 실행해 `crc=` 문자열을 찾으면 V4 여부를 판단할 수 있습니다. 문자열이 없다면 xfsprogs를 최신으로 올리고 다시 확인합니다.

폐기는 두 단계입니다. V4 mount support는 Kconfig로 build 시 끌 수 있고 이 option은 2025년 9월 default가 `no`로 바뀌었습니다. 2030년 9월에는 codebase에서 완전히 제거됩니다. 배포판은 더 일찍 지원을 철회할 수 있습니다.

Deprecated Mount Options

240-250

다음 형식의 mount 지원은 2030년 9월 제거될 예정입니다.

Name	Removal Schedule
Mounting with V4 filesystem	September 2030
Mounting ascii-ci filesystem	September 2030

Removed Mount Options

251-266

다음 mount option은 표시된 kernel version에서 이미 제거됐습니다.

Name	Removed
delaylog/nodelaylog	v4.0
ihashsize	v4.0
irixsgid	v4.0
osyncisdsync/osyncisosync	v4.0
barrier	v4.19
nobarrier	v4.19
ikeep/noikeep	v6.18
attr2/noattr2	v6.18

sysctls

267-349

다음 XFS sysctl을 사용할 수 있습니다. 범위 열은 `Min / Default / Max` 순서입니다.

sysctl	범위	설명
`fs.xfs.stats_clear`	0 / 0 / 1	`1`을 쓰면 `/proc/fs/xfs/stat`의 누적 XFS 통계를 지우고 즉시 `0`으로 돌아갑니다.
`fs.xfs.xfssyncd_centisecs`	100 / 3000 / 720000	metadata를 disk로 flush하고 내부 cache cleanup을 실행하는 간격입니다.
`fs.xfs.filestream_centisecs`	1 / 3000 / 360000	filestream cache reference를 age하고 timeout된 AG를 free stream pool로 돌리는 간격입니다.
`fs.xfs.speculative_prealloc_lifetime`	1 / 300 / 86400 seconds	unused speculative preallocation이 있는 inode를 background scan하는 간격입니다. clean inode의 미사용 공간을 free pool로 돌립니다.
`fs.xfs.error_level`	0 / 3 / 11	내부 error 보고량입니다. shutdown의 상세 message와 backtrace 등을 제어하며 threshold는 `XFS_ERRLEVEL_OFF=0`, `LOW=1`, `HIGH=5`입니다.
`fs.xfs.panic_mask`	0 / 0 / 511	선택한 error가 `BUG()`를 부르게 하는 debugging 전용 bitmask입니다. `XFS_PTAG_IFLUSH`부터 `XFS_PTAG_VERIFIER_ERROR`까지 tag를 OR합니다.
`fs.xfs.inherit_sync`	0 / 1 / 1	xfs_io(8) chattr로 directory에 준 `sync` flag를 내부 file에 상속합니다.
`fs.xfs.inherit_nodump`	0 / 1 / 1	directory의 `nodump` flag를 file에 상속합니다.
`fs.xfs.inherit_noatime`	0 / 1 / 1	directory의 `noatime` flag를 file에 상속합니다.
`fs.xfs.inherit_nosymlinks`	0 / 1 / 1	directory의 `nosymlinks` flag를 file에 상속합니다.
`fs.xfs.inherit_nodefrag`	0 / 1 / 1	directory의 `nodefrag` flag를 file에 상속합니다.
`fs.xfs.rotorstep`	1 / 1 / 256	`inode32` mode에서 다음 allocation group으로 이동하기 전 같은 AG에 배치하려는 file 수를 정해 새 file extent 할당의 AG 이동 속도를 제어합니다.

`fs.xfs.panic_mask`의 tag는 `XFS_NO_PTAG=0`, `XFS_PTAG_IFLUSH=0x00000001`, `LOGRES=0x00000002`, `AILDELETE=0x00000004`, `ERROR_REPORT=0x00000008`, `SHUTDOWN_CORRUPT=0x00000010`, `SHUTDOWN_IOERROR=0x00000020`, `SHUTDOWN_LOGERROR=0x00000040`, `FSBLOCK_ZERO=0x00000080`, `VERIFIER_ERROR=0x00000100`입니다.

Deprecated Sysctls

350-354

현재 deprecated sysctl은 없습니다.

Removed Sysctls

355-367

다음 sysctl은 표시된 kernel version에서 제거됐습니다.

Name	Removed
fs.xfs.xfsbufd_centisec	v4.0
fs.xfs.age_buffer_centisecs	v4.0
fs.xfs.irix_symlink_mode	v6.18
fs.xfs.irix_sgid_inherit	v6.18
fs.xfs.speculative_cow_prealloc_lifetime	v6.18

Error handling

368-489

XFS는 발견한 error 종류에 따라 다르게 동작합니다. failure speed는 error를 즉시, 정해진 retry 횟수 뒤, 정해진 시간 뒤에 위로 전달할지 또는 영원히 retry할지 정합니다. error class는 metadata I/O나 memory allocation처럼 설정이 적용될 subsystem을 뜻하고, error handler는 특정 error의 동작을 정의합니다.

동작은 `sysfs` file로 설정하며 각 handler는 독립적입니다. 한 class의 handler 조건 중 먼저 충족된 것이 error를 reset·retry하지 않고 전달합니다. 전달 뒤에는 context에 따라 unrecoverable shutdown, userspace 반환, 또는 unmount 중처럼 보고할 곳이 없어 무시될 수 있습니다.

mount된 filesystem마다 설정은 `/sys/fs/xfs/<dev>/error/<class>/<error>/` 아래에 있습니다. `<dev>`는 `XFS(<dev>): ...` kernel error message와 같은 짧은 device name, `<class>`는 subsystem이며 4.9 기준 `metadata` class가 metadata buffer write I/O에 적용됩니다. `<error>`는 개별 handler입니다.

top-level `/sys/fs/xfs/<dev>/error/`의 `fail_at_unmount` 범위는 0~1, 기본은 1입니다. `1`이면 unmount 중 다른 설정을 무시하고 retry와 timeout 없는 immediate fail로 바꿔 persistent error가 있어도 unmount를 끝냅니다.

`fail_at_unmount=0`이면 retry·timeout이 소진될 때까지 설정대로 계속해 unmount가 늦어지거나 `retry forever` 때문에 끝나지 않을 수 있습니다. unmount가 진행되면 sysfs entry가 먼저 사라질 수 있으므로 hang을 막을 값은 시작 전에 설정해야 합니다.

각 class에는 특정 error handler와 그 밖의 error용 `default` handler가 있습니다. 여러 retry constraint를 함께 설정하면 먼저 만료된 조건이 error를 전달합니다. 개별 directory의 `max_retries` 범위는 -1부터 INTMAX입니다.

`max_retries=-1`: 해당 error를 영원히 retry
`max_retries=0`: error가 보고되면 즉시 실패
`max_retries=N`: 전달하기 전에 N번 retry; 성공하면 해당 context의 count reset
`retry_timeout_seconds=-1`: 영원히 retry
`retry_timeout_seconds=0`: 즉시 실패
`retry_timeout_seconds=N`: 최대 N초 retry한 뒤 전달

기본값은 class와 error context에 따라 다릅니다. 예를 들어 `metadata/ENODEV`는 retry해도 회복할 수 없는 fatal error이므로 `-1`이 아니라 `0`, 즉 immediate fail이 기본입니다.

Workqueue Concurrency

490-531

XFS는 kernel workqueue로 metadata update를 병렬화해 여러 I/O를 동시에 처리하는 storage hardware를 활용합니다. 이 interface는 내부 구현 detail이며 userspace API/ABI 보장 대상이 아닙니다. 진단과 tuning 목적으로만 제공되고 언제든 바뀔 수 있습니다.

filesystem workqueue knob은 task와 data device의 짧은 이름으로 `/sys/bus/workqueue/devices/${task}!${device}`에 있습니다.

Task	Description
xfs_iwalk-$pid	filesystem 전체 inode scan. 현재 mount-time quotacheck로 제한
xfs-gc	EOF 밖 speculative allocation 또는 copy-on-write staging에 쓰고 남은 disk space의 background garbage collection

예를 들어 `/dev/nvme0n1`의 quotacheck workqueue는 `/sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/`에 있습니다.

Knob	Description
max_active	작업을 실행하도록 시작할 수 있는 background thread 최대 수
cpumask	thread 실행이 허용된 CPU
nice	thread scheduling 상대 priority. userspace process와 같은 nice level

Zoned Filesystems

532-551

zoned filesystem은 `/sys/fs/xfs/<dev>/zoned/`에 attribute를 노출합니다.

attribute	범위	설명
max_open_zones	Min 1 / Default varies / Max UINTMAX	data placement에 사용할 수 있는 open zone 최대 수를 보여 주는 read-only 값입니다. mount 때 backing zoned device capability, filesystem 크기, `max_open_zones` mount option으로 결정합니다.
zonegc_low_space	Min 0 / Default 0 / Max 100	GC가 write용으로 유지할 unused space 비율입니다. 높이면 unused block 공간을 더 회수해 burst 여유를 늘리지만 write amplification이 커집니다. 값과 무관하게 data placement용 `max_open_zones`를 열 수 있는 최소 block은 항상 확보합니다.