1What: /sys/block/<disk>/alignment_offset 2Date: April 2009 3Contact: Martin K. Petersen <martin.petersen@oracle.com> 4Description: 5 Storage devices may report a physical block size that is 6 bigger than the logical block size (for instance a drive 7 with 4KB physical sectors exposing 512-byte logical 8 blocks to the operating system). This parameter 9 indicates how many bytes the beginning of the device is 10 offset from the disk's natural alignment. 11 12 13What: /sys/block/<disk>/discard_alignment 14Date: May 2011 15Contact: Martin K. Petersen <martin.petersen@oracle.com> 16Description: 17 Devices that support discard functionality may 18 internally allocate space in units that are bigger than 19 the exported logical block size. The discard_alignment 20 parameter indicates how many bytes the beginning of the 21 device is offset from the internal allocation unit's 22 natural alignment. 23 24What: /sys/block/<disk>/atomic_write_max_bytes 25Date: February 2024 26Contact: Himanshu Madhani <himanshu.madhani@oracle.com> 27Description: 28 [RO] This parameter specifies the maximum atomic write 29 size reported by the device. This parameter is relevant 30 for merging of writes, where a merged atomic write 31 operation must not exceed this number of bytes. 32 This parameter may be greater than the value in 33 atomic_write_unit_max_bytes as 34 atomic_write_unit_max_bytes will be rounded down to a 35 power-of-two and atomic_write_unit_max_bytes may also be 36 limited by some other queue limits, such as max_segments. 37 This parameter - along with atomic_write_unit_min_bytes 38 and atomic_write_unit_max_bytes - will not be larger than 39 max_hw_sectors_kb, but may be larger than max_sectors_kb. 40 41 42What: /sys/block/<disk>/atomic_write_unit_min_bytes 43Date: February 2024 44Contact: Himanshu Madhani <himanshu.madhani@oracle.com> 45Description: 46 [RO] This parameter specifies the smallest block which can 47 be written atomically with an atomic write operation. All 48 atomic write operations must begin at a 49 atomic_write_unit_min boundary and must be multiples of 50 atomic_write_unit_min. This value must be a power-of-two. 51 52 53What: /sys/block/<disk>/atomic_write_unit_max_bytes 54Date: February 2024 55Contact: Himanshu Madhani <himanshu.madhani@oracle.com> 56Description: 57 [RO] This parameter defines the largest block which can be 58 written atomically with an atomic write operation. This 59 value must be a multiple of atomic_write_unit_min and must 60 be a power-of-two. This value will not be larger than 61 atomic_write_max_bytes. 62 63 64What: /sys/block/<disk>/atomic_write_boundary_bytes 65Date: February 2024 66Contact: Himanshu Madhani <himanshu.madhani@oracle.com> 67Description: 68 [RO] A device may need to internally split an atomic write I/O 69 which straddles a given logical block address boundary. This 70 parameter specifies the size in bytes of the atomic boundary if 71 one is reported by the device. This value must be a 72 power-of-two and at least the size as in 73 atomic_write_unit_max_bytes. 74 Any attempt to merge atomic write I/Os must not result in a 75 merged I/O which crosses this boundary (if any). 76 77 78What: /sys/block/<disk>/diskseq 79Date: February 2021 80Contact: Matteo Croce <teknoraver@meta.com> 81Description: 82 The /sys/block/<disk>/diskseq files reports the disk 83 sequence number, which is a monotonically increasing 84 number assigned to every drive. 85 Some devices, like the loop device, refresh such number 86 every time the backing file is changed. 87 The value type is 64 bit unsigned. 88 89 90What: /sys/block/<disk>/inflight 91Date: October 2009 92Contact: Jens Axboe <axboe@kernel.dk>, Nikanth Karthikesan <knikanth@suse.de> 93Description: 94 Reports the number of I/O requests currently in progress 95 (pending / in flight) in a device driver. This can be less 96 than the number of requests queued in the block device queue. 97 The report contains 2 fields: one for read requests 98 and one for write requests. 99 The value type is unsigned int. 100 Cf. Documentation/block/stat.rst which contains a single value for 101 requests in flight. 102 This is related to /sys/block/<disk>/queue/nr_requests 103 and for SCSI device also its queue_depth. 104 105 106What: /sys/block/<disk>/integrity/device_is_integrity_capable 107Date: July 2014 108Contact: Martin K. Petersen <martin.petersen@oracle.com> 109Description: 110 Indicates whether a storage device is capable of storing 111 integrity metadata. Set if the device is T10 PI-capable. 112 This flag is set to 1 if the storage media is formatted 113 with T10 Protection Information. If the storage media is 114 not formatted with T10 Protection Information, this flag 115 is set to 0. 116 117 118What: /sys/block/<disk>/integrity/format 119Date: June 2008 120Contact: Martin K. Petersen <martin.petersen@oracle.com> 121Description: 122 Metadata format for integrity capable block device. 123 E.g. T10-DIF-TYPE1-CRC. 124 This field describes the type of T10 Protection Information 125 that the block device can send and receive. 126 If the device can store application integrity metadata but 127 no T10 Protection Information profile is used, this field 128 contains "nop". 129 If the device does not support integrity metadata, this 130 field contains "none". 131 132 133What: /sys/block/<disk>/integrity/protection_interval_bytes 134Date: July 2015 135Contact: Martin K. Petersen <martin.petersen@oracle.com> 136Description: 137 Describes the number of data bytes which are protected 138 by one integrity tuple. Typically the device's logical 139 block size. 140 141 142What: /sys/block/<disk>/integrity/read_verify 143Date: June 2008 144Contact: Martin K. Petersen <martin.petersen@oracle.com> 145Description: 146 Indicates whether the block layer should verify the 147 integrity of read requests serviced by devices that 148 support sending integrity metadata. 149 150 151What: /sys/block/<disk>/integrity/tag_size 152Date: June 2008 153Contact: Martin K. Petersen <martin.petersen@oracle.com> 154Description: 155 Number of bytes of integrity tag space available per 156 protection_interval_bytes, which is typically 157 the device's logical block size. 158 This field describes the size of the application tag 159 if the storage device is formatted with T10 Protection 160 Information and permits use of the application tag. 161 The tag_size is reported in bytes and indicates the 162 space available for adding an opaque tag to each block 163 (protection_interval_bytes). 164 If the device does not support T10 Protection Information 165 (even if the device provides application integrity 166 metadata space), this field is set to 0. 167 168 169What: /sys/block/<disk>/integrity/write_generate 170Date: June 2008 171Contact: Martin K. Petersen <martin.petersen@oracle.com> 172Description: 173 Indicates whether the block layer should automatically 174 generate checksums for write requests bound for 175 devices that support receiving integrity metadata. 176 177 178What: /sys/block/<disk>/partscan 179Date: May 2024 180Contact: Christoph Hellwig <hch@lst.de> 181Description: 182 The /sys/block/<disk>/partscan files reports if partition 183 scanning is enabled for the disk. It returns "1" if partition 184 scanning is enabled, or "0" if not. The value type is a 32-bit 185 unsigned integer, but only "0" and "1" are valid values. 186 187 188What: /sys/block/<disk>/<partition>/alignment_offset 189Date: April 2009 190Contact: Martin K. Petersen <martin.petersen@oracle.com> 191Description: 192 Storage devices may report a physical block size that is 193 bigger than the logical block size (for instance a drive 194 with 4KB physical sectors exposing 512-byte logical 195 blocks to the operating system). This parameter 196 indicates how many bytes the beginning of the partition 197 is offset from the disk's natural alignment. 198 199 200What: /sys/block/<disk>/<partition>/discard_alignment 201Date: May 2011 202Contact: Martin K. Petersen <martin.petersen@oracle.com> 203Description: 204 Devices that support discard functionality may 205 internally allocate space in units that are bigger than 206 the exported logical block size. The discard_alignment 207 parameter indicates how many bytes the beginning of the 208 partition is offset from the internal allocation unit's 209 natural alignment. 210 211 212What: /sys/block/<disk>/<partition>/stat 213Date: February 2008 214Contact: Jerome Marchand <jmarchan@redhat.com> 215Description: 216 The /sys/block/<disk>/<partition>/stat files display the 217 I/O statistics of partition <partition>. The format is the 218 same as the format of /sys/block/<disk>/stat. 219 220 221What: /sys/block/<disk>/queue/add_random 222Date: June 2010 223Contact: linux-block@vger.kernel.org 224Description: 225 [RW] This file allows to turn off the disk entropy contribution. 226 Default value of this file is '1'(on). 227 228 229What: /sys/block/<disk>/queue/chunk_sectors 230Date: September 2016 231Contact: Hannes Reinecke <hare@suse.com> 232Description: 233 [RO] chunk_sectors has different meaning depending on the type 234 of the disk. For a RAID device (dm-raid), chunk_sectors 235 indicates the size in 512B sectors of the RAID volume stripe 236 segment. For a zoned block device, either host-aware or 237 host-managed, chunk_sectors indicates the size in 512B sectors 238 of the zones of the device, with the eventual exception of the 239 last zone of the device which may be smaller. 240 241 242What: /sys/block/<disk>/queue/crypto/ 243Date: February 2022 244Contact: linux-block@vger.kernel.org 245Description: 246 The presence of this subdirectory of /sys/block/<disk>/queue/ 247 indicates that the device supports inline encryption. This 248 subdirectory contains files which describe the inline encryption 249 capabilities of the device. For more information about inline 250 encryption, refer to Documentation/block/inline-encryption.rst. 251 252 253What: /sys/block/<disk>/queue/crypto/hw_wrapped_keys 254Date: February 2025 255Contact: linux-block@vger.kernel.org 256Description: 257 [RO] The presence of this file indicates that the device 258 supports hardware-wrapped inline encryption keys, i.e. key blobs 259 that can only be unwrapped and used by dedicated hardware. For 260 more information about hardware-wrapped inline encryption keys, 261 see Documentation/block/inline-encryption.rst. 262 263 264What: /sys/block/<disk>/queue/crypto/max_dun_bits 265Date: February 2022 266Contact: linux-block@vger.kernel.org 267Description: 268 [RO] This file shows the maximum length, in bits, of data unit 269 numbers accepted by the device in inline encryption requests. 270 271 272What: /sys/block/<disk>/queue/crypto/modes/<mode> 273Date: February 2022 274Contact: linux-block@vger.kernel.org 275Description: 276 [RO] For each crypto mode (i.e., encryption/decryption 277 algorithm) the device supports with inline encryption, a file 278 will exist at this location. It will contain a hexadecimal 279 number that is a bitmask of the supported data unit sizes, in 280 bytes, for that crypto mode. 281 282 Currently, the crypto modes that may be supported are: 283 284 * AES-256-XTS 285 * AES-128-CBC-ESSIV 286 * Adiantum 287 288 For example, if a device supports AES-256-XTS inline encryption 289 with data unit sizes of 512 and 4096 bytes, the file 290 /sys/block/<disk>/queue/crypto/modes/AES-256-XTS will exist and 291 will contain "0x1200". 292 293 294What: /sys/block/<disk>/queue/crypto/num_keyslots 295Date: February 2022 296Contact: linux-block@vger.kernel.org 297Description: 298 [RO] This file shows the number of keyslots the device has for 299 use with inline encryption. 300 301 302What: /sys/block/<disk>/queue/crypto/raw_keys 303Date: February 2025 304Contact: linux-block@vger.kernel.org 305Description: 306 [RO] The presence of this file indicates that the device 307 supports raw inline encryption keys, i.e. keys that are managed 308 in raw, plaintext form in software. 309 310 311What: /sys/block/<disk>/queue/dax 312Date: June 2016 313Contact: linux-block@vger.kernel.org 314Description: 315 [RO] This file indicates whether the device supports Direct 316 Access (DAX), used by CPU-addressable storage to bypass the 317 pagecache. It shows '1' if true, '0' if not. 318 319 320What: /sys/block/<disk>/queue/discard_granularity 321Date: May 2011 322Contact: Martin K. Petersen <martin.petersen@oracle.com> 323Description: 324 [RO] Devices that support discard functionality may internally 325 allocate space using units that are bigger than the logical 326 block size. The discard_granularity parameter indicates the size 327 of the internal allocation unit in bytes if reported by the 328 device. Otherwise the discard_granularity will be set to match 329 the device's physical block size. A discard_granularity of 0 330 means that the device does not support discard functionality. 331 332 333What: /sys/block/<disk>/queue/discard_max_bytes 334Date: May 2011 335Contact: Martin K. Petersen <martin.petersen@oracle.com> 336Description: 337 [RW] While discard_max_hw_bytes is the hardware limit for the 338 device, this setting is the software limit. Some devices exhibit 339 large latencies when large discards are issued, setting this 340 value lower will make Linux issue smaller discards and 341 potentially help reduce latencies induced by large discard 342 operations. 343 344 345What: /sys/block/<disk>/queue/discard_max_hw_bytes 346Date: July 2015 347Contact: linux-block@vger.kernel.org 348Description: 349 [RO] Devices that support discard functionality may have 350 internal limits on the number of bytes that can be trimmed or 351 unmapped in a single operation. The `discard_max_hw_bytes` 352 parameter is set by the device driver to the maximum number of 353 bytes that can be discarded in a single operation. Discard 354 requests issued to the device must not exceed this limit. A 355 `discard_max_hw_bytes` value of 0 means that the device does not 356 support discard functionality. 357 358 359What: /sys/block/<disk>/queue/discard_zeroes_data 360Date: May 2011 361Contact: Martin K. Petersen <martin.petersen@oracle.com> 362Description: 363 [RO] Will always return 0. Don't rely on any specific behavior 364 for discards, and don't read this file. 365 366 367What: /sys/block/<disk>/queue/dma_alignment 368Date: May 2022 369Contact: linux-block@vger.kernel.org 370Description: 371 Reports the alignment that user space addresses must have to be 372 used for raw block device access with O_DIRECT and other driver 373 specific passthrough mechanisms. 374 375 376What: /sys/block/<disk>/queue/fua 377Date: May 2018 378Contact: linux-block@vger.kernel.org 379Description: 380 [RO] Whether or not the block driver supports the FUA flag for 381 write requests. FUA stands for Force Unit Access. If the FUA 382 flag is set that means that write requests must bypass the 383 volatile cache of the storage device. 384 385 386What: /sys/block/<disk>/queue/hw_sector_size 387Date: January 2008 388Contact: linux-block@vger.kernel.org 389Description: 390 [RO] This is the hardware sector size of the device, in bytes. 391 392 393What: /sys/block/<disk>/queue/independent_access_ranges/ 394Date: October 2021 395Contact: linux-block@vger.kernel.org 396Description: 397 [RO] The presence of this sub-directory of the 398 /sys/block/xxx/queue/ directory indicates that the device is 399 capable of executing requests targeting different sector ranges 400 in parallel. For instance, single LUN multi-actuator hard-disks 401 will have an independent_access_ranges directory if the device 402 correctly advertises the sector ranges of its actuators. 403 404 The independent_access_ranges directory contains one directory 405 per access range, with each range described using the sector 406 (RO) attribute file to indicate the first sector of the range 407 and the nr_sectors (RO) attribute file to indicate the total 408 number of sectors in the range starting from the first sector of 409 the range. For example, a dual-actuator hard-disk will have the 410 following independent_access_ranges entries.:: 411 412 $ tree /sys/block/<disk>/queue/independent_access_ranges/ 413 /sys/block/<disk>/queue/independent_access_ranges/ 414 |-- 0 415 | |-- nr_sectors 416 | `-- sector 417 `-- 1 418 |-- nr_sectors 419 `-- sector 420 421 The sector and nr_sectors attributes use 512B sector unit, 422 regardless of the actual block size of the device. Independent 423 access ranges do not overlap and include all sectors within the 424 device capacity. The access ranges are numbered in increasing 425 order of the range start sector, that is, the sector attribute 426 of range 0 always has the value 0. 427 428 429What: /sys/block/<disk>/queue/io_poll 430Date: November 2015 431Contact: linux-block@vger.kernel.org 432Description: 433 [RW] When read, this file shows whether polling is enabled (1) 434 or disabled (0). Writing '0' to this file will disable polling 435 for this device. Writing any non-zero value will enable this 436 feature. 437 438 439What: /sys/block/<disk>/queue/io_poll_delay 440Date: November 2016 441Contact: linux-block@vger.kernel.org 442Description: 443 [RW] This was used to control what kind of polling will be 444 performed. It is now fixed to -1, which is classic polling. 445 In this mode, the CPU will repeatedly ask for completions 446 without giving up any time. 447 <deprecated> 448 449 450What: /sys/block/<disk>/queue/io_timeout 451Date: November 2018 452Contact: Weiping Zhang <zhangweiping@didiglobal.com> 453Description: 454 [RW] io_timeout is the request timeout in milliseconds. If a 455 request does not complete in this time then the block driver 456 timeout handler is invoked. That timeout handler can decide to 457 retry the request, to fail it or to start a device recovery 458 strategy. 459 460 461What: /sys/block/<disk>/queue/iostats 462Date: January 2009 463Contact: linux-block@vger.kernel.org 464Description: 465 [RW] This file is used to control (on/off) the iostats 466 accounting of the disk. 467 468What: /sys/block/<disk>/queue/iostats_passthrough 469Date: October 2024 470Contact: linux-block@vger.kernel.org 471Description: 472 [RW] This file is used to control (on/off) the iostats 473 accounting of the disk for passthrough commands. 474 475 476What: /sys/block/<disk>/queue/logical_block_size 477Date: May 2009 478Contact: Martin K. Petersen <martin.petersen@oracle.com> 479Description: 480 [RO] This is the smallest unit the storage device can address. 481 It is typically 512 bytes. 482 483 484What: /sys/block/<disk>/queue/max_active_zones 485Date: July 2020 486Contact: Niklas Cassel <niklas.cassel@wdc.com> 487Description: 488 [RO] For zoned block devices (zoned attribute indicating 489 "host-managed" or "host-aware"), the sum of zones belonging to 490 any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED, 491 is limited by this value. If this value is 0, there is no limit. 492 493 If the host attempts to exceed this limit, the driver should 494 report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user 495 space may see as the EOVERFLOW errno. 496 497 498What: /sys/block/<disk>/queue/max_discard_segments 499Date: February 2017 500Contact: linux-block@vger.kernel.org 501Description: 502 [RO] The maximum number of DMA scatter/gather entries in a 503 discard request. 504 505 506What: /sys/block/<disk>/queue/max_hw_sectors_kb 507Date: September 2004 508Contact: linux-block@vger.kernel.org 509Description: 510 [RO] This is the maximum number of kilobytes supported in a 511 single data transfer. 512 513 514What: /sys/block/<disk>/queue/max_integrity_segments 515Date: September 2010 516Contact: linux-block@vger.kernel.org 517Description: 518 [RO] Maximum number of elements in a DMA scatter/gather list 519 with integrity data that will be submitted by the block layer 520 core to the associated block driver. 521 522 523What: /sys/block/<disk>/queue/max_open_zones 524Date: July 2020 525Contact: Niklas Cassel <niklas.cassel@wdc.com> 526Description: 527 [RO] For zoned block devices (zoned attribute indicating 528 "host-managed" or "host-aware"), the sum of zones belonging to 529 any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is 530 limited by this value. If this value is 0, there is no limit. 531 532 533What: /sys/block/<disk>/queue/max_sectors_kb 534Date: September 2004 535Contact: linux-block@vger.kernel.org 536Description: 537 [RW] This is the maximum number of kilobytes that the block 538 layer will allow for a filesystem request. Must be smaller than 539 or equal to the maximum size allowed by the hardware. Write 0 540 to use default kernel settings. 541 542 543What: /sys/block/<disk>/queue/max_segment_size 544Date: March 2010 545Contact: linux-block@vger.kernel.org 546Description: 547 [RO] Maximum size in bytes of a single element in a DMA 548 scatter/gather list. 549 550What: /sys/block/<disk>/queue/max_write_streams 551Date: November 2024 552Contact: linux-block@vger.kernel.org 553Description: 554 [RO] Maximum number of write streams supported, 0 if not 555 supported. If supported, valid values are 1 through 556 max_write_streams, inclusive. 557 558What: /sys/block/<disk>/queue/write_stream_granularity 559Date: November 2024 560Contact: linux-block@vger.kernel.org 561Description: 562 [RO] Granularity of a write stream in bytes. The granularity 563 of a write stream is the size that should be discarded or 564 overwritten together to avoid write amplification in the device. 565 566What: /sys/block/<disk>/queue/max_segments 567Date: March 2010 568Contact: linux-block@vger.kernel.org 569Description: 570 [RO] Maximum number of elements in a DMA scatter/gather list 571 that is submitted to the associated block driver. 572 573 574What: /sys/block/<disk>/queue/minimum_io_size 575Date: April 2009 576Contact: Martin K. Petersen <martin.petersen@oracle.com> 577Description: 578 [RO] Storage devices may report a granularity or preferred 579 minimum I/O size which is the smallest request the device can 580 perform without incurring a performance penalty. For disk 581 drives this is often the physical block size. For RAID arrays 582 it is often the stripe chunk size. A properly aligned multiple 583 of minimum_io_size is the preferred request size for workloads 584 where a high number of I/O operations is desired. 585 586 587What: /sys/block/<disk>/queue/nomerges 588Date: January 2010 589Contact: linux-block@vger.kernel.org 590Description: 591 [RW] Standard I/O elevator operations include attempts to merge 592 contiguous I/Os. For known random I/O loads these attempts will 593 always fail and result in extra cycles being spent in the 594 kernel. This allows one to turn off this behavior on one of two 595 ways: When set to 1, complex merge checks are disabled, but the 596 simple one-shot merges with the previous I/O request are 597 enabled. When set to 2, all merge tries are disabled. The 598 default value is 0 - which enables all types of merge tries. 599 600 601What: /sys/block/<disk>/queue/nr_requests 602Date: July 2003 603Contact: linux-block@vger.kernel.org 604Description: 605 [RW] This controls how many requests may be allocated in the 606 block layer. Noted this value only represents the quantity for a 607 single blk_mq_tags instance. The actual number for the entire 608 device depends on the hardware queue count, whether elevator is 609 enabled, and whether tags are shared. 610 611 612What: /sys/block/<disk>/queue/async_depth 613Date: August 2025 614Contact: linux-block@vger.kernel.org 615Description: 616 [RW] Controls how many asynchronous requests may be allocated in the 617 block layer. The value is always capped at nr_requests. 618 619 When no elevator is active (none): 620 - async_depth is always equal to nr_requests. 621 622 For bfq scheduler: 623 - By default, async_depth is set to 75% of nr_requests. 624 Internal limits are then derived from this value: 625 * Sync writes: limited to async_depth (≈75% of nr_requests). 626 * Async I/O: limited to ~2/3 of async_depth (≈50% of nr_requests). 627 628 If a bfq_queue is weight-raised: 629 * Sync writes: limited to ~1/2 of async_depth (≈37% of nr_requests). 630 * Async I/O: limited to ~1/4 of async_depth (≈18% of nr_requests). 631 632 - If the user writes a custom value to async_depth, BFQ will recompute 633 these limits proportionally based on the new value. 634 635 For Kyber: 636 - By default async_depth is set to 75% of nr_requests. 637 - If the user writes a custom value to async_depth, then it override the 638 default and directly control the limit for writes and async I/O. 639 640 For mq-deadline: 641 - By default async_depth is set to nr_requests. 642 - If the user writes a custom value to async_depth, then it override the 643 default and directly control the limit for writes and async I/O. 644 645 646What: /sys/block/<disk>/queue/nr_zones 647Date: November 2018 648Contact: Damien Le Moal <damien.lemoal@wdc.com> 649Description: 650 [RO] nr_zones indicates the total number of zones of a zoned 651 block device ("host-aware" or "host-managed" zone model). For 652 regular block devices, the value is always 0. 653 654 655What: /sys/block/<disk>/queue/optimal_io_size 656Date: April 2009 657Contact: Martin K. Petersen <martin.petersen@oracle.com> 658Description: 659 [RO] Storage devices may report an optimal I/O size, which is 660 the device's preferred unit for sustained I/O. This is rarely 661 reported for disk drives. For RAID arrays it is usually the 662 stripe width or the internal track size. A properly aligned 663 multiple of optimal_io_size is the preferred request size for 664 workloads where sustained throughput is desired. If no optimal 665 I/O size is reported this file contains 0. 666 667 668What: /sys/block/<disk>/queue/physical_block_size 669Date: May 2009 670Contact: Martin K. Petersen <martin.petersen@oracle.com> 671Description: 672 [RO] This is the smallest unit a physical storage device can 673 write atomically. It is usually the same as the logical block 674 size but may be bigger. One example is SATA drives with 4KB 675 sectors that expose a 512-byte logical block size to the 676 operating system. For stacked block devices the 677 physical_block_size variable contains the maximum 678 physical_block_size of the component devices. 679 680 681What: /sys/block/<disk>/queue/read_ahead_kb 682Date: May 2004 683Contact: linux-block@vger.kernel.org 684Description: 685 [RW] Maximum number of kilobytes to read-ahead for filesystems 686 on this block device. 687 688 For MADV_HUGEPAGE, the readahead size may exceed this setting 689 since its granularity is based on the hugepage size. 690 691 692What: /sys/block/<disk>/queue/rotational 693Date: January 2009 694Contact: linux-block@vger.kernel.org 695Description: 696 [RW] This file is used to stat if the device is of rotational 697 type or non-rotational type. 698 699 700What: /sys/block/<disk>/queue/rq_affinity 701Date: September 2008 702Contact: linux-block@vger.kernel.org 703Description: 704 [RW] If this option is '1', the block layer will migrate request 705 completions to the cpu "group" that originally submitted the 706 request. For some workloads this provides a significant 707 reduction in CPU cycles due to caching effects. 708 709 For storage configurations that need to maximize distribution of 710 completion processing setting this option to '2' forces the 711 completion to run on the requesting cpu (bypassing the "group" 712 aggregation logic). 713 714 715What: /sys/block/<disk>/queue/scheduler 716Date: October 2004 717Contact: linux-block@vger.kernel.org 718Description: 719 [RW] When read, this file will display the current and available 720 IO schedulers for this block device. The currently active IO 721 scheduler will be enclosed in [] brackets. Writing an IO 722 scheduler name to this file will switch control of this block 723 device to that new IO scheduler. Note that writing an IO 724 scheduler name to this file will attempt to load that IO 725 scheduler module, if it isn't already present in the system. 726 727 728What: /sys/block/<disk>/queue/stable_writes 729Date: September 2020 730Contact: linux-block@vger.kernel.org 731Description: 732 [RW] This file will contain '1' if memory must not be modified 733 while it is being used in a write request to this device. When 734 this is the case and the kernel is performing writeback of a 735 page, the kernel will wait for writeback to complete before 736 allowing the page to be modified again, rather than allowing 737 immediate modification as is normally the case. This 738 restriction arises when the device accesses the memory multiple 739 times where the same data must be seen every time -- for 740 example, once to calculate a checksum and once to actually write 741 the data. If no such restriction exists, this file will contain 742 '0'. This file is writable for testing purposes. 743 744What: /sys/block/<disk>/queue/virt_boundary_mask 745Date: April 2021 746Contact: linux-block@vger.kernel.org 747Description: 748 [RO] This file shows the I/O segment memory alignment mask for 749 the block device. I/O requests to this device will be split 750 between segments wherever either the memory address of the end 751 of the previous segment or the memory address of the beginning 752 of the current segment is not aligned to virt_boundary_mask + 1 753 bytes. 754 755 756What: /sys/block/<disk>/queue/wbt_lat_usec 757Date: November 2016 758Contact: linux-block@vger.kernel.org 759Description: 760 [RW] If the device is registered for writeback throttling, then 761 this file shows the target minimum read latency. If this latency 762 is exceeded in a given window of time (see curr_win_nsec), then 763 the writeback throttling will start scaling back writes. Writing 764 a value of '0' to this file disables the feature. Writing a 765 value of '-1' to this file resets the value to the default 766 setting. 767 768 769What: /sys/block/<disk>/queue/write_cache 770Date: April 2016 771Contact: linux-block@vger.kernel.org 772Description: 773 [RW] When read, this file will display whether the device has 774 write back caching enabled or not. It will return "write back" 775 for the former case, and "write through" for the latter. Writing 776 to this file can change the kernels view of the device, but it 777 doesn't alter the device state. This means that it might not be 778 safe to toggle the setting from "write back" to "write through", 779 since that will also eliminate cache flushes issued by the 780 kernel. 781 782 783What: /sys/block/<disk>/queue/write_same_max_bytes 784Date: January 2012 785Contact: Martin K. Petersen <martin.petersen@oracle.com> 786Description: 787 [RO] Some devices support a write same operation in which a 788 single data block can be written to a range of several 789 contiguous blocks on storage. This can be used to wipe areas on 790 disk or to initialize drives in a RAID configuration. 791 write_same_max_bytes indicates how many bytes can be written in 792 a single write same command. If write_same_max_bytes is 0, write 793 same is not supported by the device. 794 795 796What: /sys/block/<disk>/queue/write_zeroes_max_bytes 797Date: November 2016 798Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> 799Description: 800 [RO] Devices that support write zeroes operation in which a 801 single request can be issued to zero out the range of contiguous 802 blocks on storage without having any payload in the request. 803 This can be used to optimize writing zeroes to the devices. 804 write_zeroes_max_bytes indicates how many bytes can be written 805 in a single write zeroes command. If write_zeroes_max_bytes is 806 0, write zeroes is not supported by the device. 807 808 809What: /sys/block/<disk>/queue/write_zeroes_unmap_max_hw_bytes 810Date: January 2025 811Contact: Zhang Yi <yi.zhang@huawei.com> 812Description: 813 [RO] This file indicates whether a device supports zeroing data 814 in a specified block range without incurring the cost of 815 physically writing zeroes to the media for each individual 816 block. If this parameter is set to write_zeroes_max_bytes, the 817 device implements a zeroing operation which opportunistically 818 avoids writing zeroes to media while still guaranteeing that 819 subsequent reads from the specified block range will return 820 zeroed data. This operation is a best-effort optimization, a 821 device may fall back to physically writing zeroes to the media 822 due to other factors such as misalignment or being asked to 823 clear a block range smaller than the device's internal 824 allocation unit. If this parameter is set to 0, the device may 825 have to write each logical block media during a zeroing 826 operation. 827 828 829What: /sys/block/<disk>/queue/write_zeroes_unmap_max_bytes 830Date: January 2025 831Contact: Zhang Yi <yi.zhang@huawei.com> 832Description: 833 [RW] While write_zeroes_unmap_max_hw_bytes is the hardware limit 834 for the device, this setting is the software limit. Since the 835 unmap write zeroes operation is a best-effort optimization, some 836 devices may still physically writing zeroes to media. So the 837 speed of this operation is not guaranteed. Writing a value of 838 '0' to this file disables this operation. Otherwise, this 839 parameter should be equal to write_zeroes_unmap_max_hw_bytes. 840 841 842What: /sys/block/<disk>/queue/zone_append_max_bytes 843Date: May 2020 844Contact: linux-block@vger.kernel.org 845Description: 846 [RO] This is the maximum number of bytes that can be written to 847 a sequential zone of a zoned block device using a zone append 848 write operation (REQ_OP_ZONE_APPEND). This value is always 0 for 849 regular block devices. 850 851 852What: /sys/block/<disk>/queue/zone_write_granularity 853Date: January 2021 854Contact: linux-block@vger.kernel.org 855Description: 856 [RO] This indicates the alignment constraint, in bytes, for 857 write operations in sequential zones of zoned block devices 858 (devices with a zoned attributed that reports "host-managed" or 859 "host-aware"). This value is always 0 for regular block devices. 860 861 862What: /sys/block/<disk>/queue/zoned 863Date: September 2016 864Contact: Damien Le Moal <damien.lemoal@wdc.com> 865Description: 866 [RO] zoned indicates if the device is a zoned block device and 867 the zone model of the device if it is indeed zoned. The 868 possible values indicated by zoned are "none" for regular block 869 devices and "host-aware" or "host-managed" for zoned block 870 devices. The characteristics of host-aware and host-managed 871 zoned block devices are described in the ZBC (Zoned Block 872 Commands) and ZAC (Zoned Device ATA Command Set) standards. 873 These standards also define the "drive-managed" zone model. 874 However, since drive-managed zoned block devices do not support 875 zone commands, they will be treated as regular block devices and 876 zoned will report "none". 877 878 879What: /sys/block/<disk>/hidden 880Date: March 2023 881Contact: linux-block@vger.kernel.org 882Description: 883 [RO] the block device is hidden. it doesn’t produce events, and 884 can’t be opened from userspace or using blkdev_get*. 885 Used for the underlying components of multipath devices. 886 887 888What: /sys/block/<disk>/stat 889Date: February 2008 890Contact: Jerome Marchand <jmarchan@redhat.com> 891Description: 892 The /sys/block/<disk>/stat files displays the I/O 893 statistics of disk <disk>. They contain 11 fields: 894 895 == ============================================== 896 1 reads completed successfully 897 2 reads merged 898 3 sectors read 899 4 time spent reading (ms) 900 5 writes completed 901 6 writes merged 902 7 sectors written 903 8 time spent writing (ms) 904 9 I/Os currently in progress 905 10 time spent doing I/Os (ms) 906 11 weighted time spent doing I/Os (ms) 907 12 discards completed 908 13 discards merged 909 14 sectors discarded 910 15 time spent discarding (ms) 911 16 flush requests completed 912 17 time spent flushing (ms) 913 == ============================================== 914 915 For more details refer Documentation/admin-guide/iostats.rst 916