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 <mcroce@microsoft.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. 112 113 114What: /sys/block/<disk>/integrity/format 115Date: June 2008 116Contact: Martin K. Petersen <martin.petersen@oracle.com> 117Description: 118 Metadata format for integrity capable block device. 119 E.g. T10-DIF-TYPE1-CRC. 120 121 122What: /sys/block/<disk>/integrity/protection_interval_bytes 123Date: July 2015 124Contact: Martin K. Petersen <martin.petersen@oracle.com> 125Description: 126 Describes the number of data bytes which are protected 127 by one integrity tuple. Typically the device's logical 128 block size. 129 130 131What: /sys/block/<disk>/integrity/read_verify 132Date: June 2008 133Contact: Martin K. Petersen <martin.petersen@oracle.com> 134Description: 135 Indicates whether the block layer should verify the 136 integrity of read requests serviced by devices that 137 support sending integrity metadata. 138 139 140What: /sys/block/<disk>/integrity/tag_size 141Date: June 2008 142Contact: Martin K. Petersen <martin.petersen@oracle.com> 143Description: 144 Number of bytes of integrity tag space available per 145 512 bytes of data. 146 147 148What: /sys/block/<disk>/integrity/write_generate 149Date: June 2008 150Contact: Martin K. Petersen <martin.petersen@oracle.com> 151Description: 152 Indicates whether the block layer should automatically 153 generate checksums for write requests bound for 154 devices that support receiving integrity metadata. 155 156 157What: /sys/block/<disk>/partscan 158Date: May 2024 159Contact: Christoph Hellwig <hch@lst.de> 160Description: 161 The /sys/block/<disk>/partscan files reports if partition 162 scanning is enabled for the disk. It returns "1" if partition 163 scanning is enabled, or "0" if not. The value type is a 32-bit 164 unsigned integer, but only "0" and "1" are valid values. 165 166 167What: /sys/block/<disk>/<partition>/alignment_offset 168Date: April 2009 169Contact: Martin K. Petersen <martin.petersen@oracle.com> 170Description: 171 Storage devices may report a physical block size that is 172 bigger than the logical block size (for instance a drive 173 with 4KB physical sectors exposing 512-byte logical 174 blocks to the operating system). This parameter 175 indicates how many bytes the beginning of the partition 176 is offset from the disk's natural alignment. 177 178 179What: /sys/block/<disk>/<partition>/discard_alignment 180Date: May 2011 181Contact: Martin K. Petersen <martin.petersen@oracle.com> 182Description: 183 Devices that support discard functionality may 184 internally allocate space in units that are bigger than 185 the exported logical block size. The discard_alignment 186 parameter indicates how many bytes the beginning of the 187 partition is offset from the internal allocation unit's 188 natural alignment. 189 190 191What: /sys/block/<disk>/<partition>/stat 192Date: February 2008 193Contact: Jerome Marchand <jmarchan@redhat.com> 194Description: 195 The /sys/block/<disk>/<partition>/stat files display the 196 I/O statistics of partition <partition>. The format is the 197 same as the format of /sys/block/<disk>/stat. 198 199 200What: /sys/block/<disk>/queue/add_random 201Date: June 2010 202Contact: linux-block@vger.kernel.org 203Description: 204 [RW] This file allows to turn off the disk entropy contribution. 205 Default value of this file is '1'(on). 206 207 208What: /sys/block/<disk>/queue/chunk_sectors 209Date: September 2016 210Contact: Hannes Reinecke <hare@suse.com> 211Description: 212 [RO] chunk_sectors has different meaning depending on the type 213 of the disk. For a RAID device (dm-raid), chunk_sectors 214 indicates the size in 512B sectors of the RAID volume stripe 215 segment. For a zoned block device, either host-aware or 216 host-managed, chunk_sectors indicates the size in 512B sectors 217 of the zones of the device, with the eventual exception of the 218 last zone of the device which may be smaller. 219 220 221What: /sys/block/<disk>/queue/crypto/ 222Date: February 2022 223Contact: linux-block@vger.kernel.org 224Description: 225 The presence of this subdirectory of /sys/block/<disk>/queue/ 226 indicates that the device supports inline encryption. This 227 subdirectory contains files which describe the inline encryption 228 capabilities of the device. For more information about inline 229 encryption, refer to Documentation/block/inline-encryption.rst. 230 231 232What: /sys/block/<disk>/queue/crypto/max_dun_bits 233Date: February 2022 234Contact: linux-block@vger.kernel.org 235Description: 236 [RO] This file shows the maximum length, in bits, of data unit 237 numbers accepted by the device in inline encryption requests. 238 239 240What: /sys/block/<disk>/queue/crypto/modes/<mode> 241Date: February 2022 242Contact: linux-block@vger.kernel.org 243Description: 244 [RO] For each crypto mode (i.e., encryption/decryption 245 algorithm) the device supports with inline encryption, a file 246 will exist at this location. It will contain a hexadecimal 247 number that is a bitmask of the supported data unit sizes, in 248 bytes, for that crypto mode. 249 250 Currently, the crypto modes that may be supported are: 251 252 * AES-256-XTS 253 * AES-128-CBC-ESSIV 254 * Adiantum 255 256 For example, if a device supports AES-256-XTS inline encryption 257 with data unit sizes of 512 and 4096 bytes, the file 258 /sys/block/<disk>/queue/crypto/modes/AES-256-XTS will exist and 259 will contain "0x1200". 260 261 262What: /sys/block/<disk>/queue/crypto/num_keyslots 263Date: February 2022 264Contact: linux-block@vger.kernel.org 265Description: 266 [RO] This file shows the number of keyslots the device has for 267 use with inline encryption. 268 269 270What: /sys/block/<disk>/queue/dax 271Date: June 2016 272Contact: linux-block@vger.kernel.org 273Description: 274 [RO] This file indicates whether the device supports Direct 275 Access (DAX), used by CPU-addressable storage to bypass the 276 pagecache. It shows '1' if true, '0' if not. 277 278 279What: /sys/block/<disk>/queue/discard_granularity 280Date: May 2011 281Contact: Martin K. Petersen <martin.petersen@oracle.com> 282Description: 283 [RO] Devices that support discard functionality may internally 284 allocate space using units that are bigger than the logical 285 block size. The discard_granularity parameter indicates the size 286 of the internal allocation unit in bytes if reported by the 287 device. Otherwise the discard_granularity will be set to match 288 the device's physical block size. A discard_granularity of 0 289 means that the device does not support discard functionality. 290 291 292What: /sys/block/<disk>/queue/discard_max_bytes 293Date: May 2011 294Contact: Martin K. Petersen <martin.petersen@oracle.com> 295Description: 296 [RW] While discard_max_hw_bytes is the hardware limit for the 297 device, this setting is the software limit. Some devices exhibit 298 large latencies when large discards are issued, setting this 299 value lower will make Linux issue smaller discards and 300 potentially help reduce latencies induced by large discard 301 operations. 302 303 304What: /sys/block/<disk>/queue/discard_max_hw_bytes 305Date: July 2015 306Contact: linux-block@vger.kernel.org 307Description: 308 [RO] Devices that support discard functionality may have 309 internal limits on the number of bytes that can be trimmed or 310 unmapped in a single operation. The `discard_max_hw_bytes` 311 parameter is set by the device driver to the maximum number of 312 bytes that can be discarded in a single operation. Discard 313 requests issued to the device must not exceed this limit. A 314 `discard_max_hw_bytes` value of 0 means that the device does not 315 support discard functionality. 316 317 318What: /sys/block/<disk>/queue/discard_zeroes_data 319Date: May 2011 320Contact: Martin K. Petersen <martin.petersen@oracle.com> 321Description: 322 [RO] Will always return 0. Don't rely on any specific behavior 323 for discards, and don't read this file. 324 325 326What: /sys/block/<disk>/queue/dma_alignment 327Date: May 2022 328Contact: linux-block@vger.kernel.org 329Description: 330 Reports the alignment that user space addresses must have to be 331 used for raw block device access with O_DIRECT and other driver 332 specific passthrough mechanisms. 333 334 335What: /sys/block/<disk>/queue/fua 336Date: May 2018 337Contact: linux-block@vger.kernel.org 338Description: 339 [RO] Whether or not the block driver supports the FUA flag for 340 write requests. FUA stands for Force Unit Access. If the FUA 341 flag is set that means that write requests must bypass the 342 volatile cache of the storage device. 343 344 345What: /sys/block/<disk>/queue/hw_sector_size 346Date: January 2008 347Contact: linux-block@vger.kernel.org 348Description: 349 [RO] This is the hardware sector size of the device, in bytes. 350 351 352What: /sys/block/<disk>/queue/independent_access_ranges/ 353Date: October 2021 354Contact: linux-block@vger.kernel.org 355Description: 356 [RO] The presence of this sub-directory of the 357 /sys/block/xxx/queue/ directory indicates that the device is 358 capable of executing requests targeting different sector ranges 359 in parallel. For instance, single LUN multi-actuator hard-disks 360 will have an independent_access_ranges directory if the device 361 correctly advertises the sector ranges of its actuators. 362 363 The independent_access_ranges directory contains one directory 364 per access range, with each range described using the sector 365 (RO) attribute file to indicate the first sector of the range 366 and the nr_sectors (RO) attribute file to indicate the total 367 number of sectors in the range starting from the first sector of 368 the range. For example, a dual-actuator hard-disk will have the 369 following independent_access_ranges entries.:: 370 371 $ tree /sys/block/<disk>/queue/independent_access_ranges/ 372 /sys/block/<disk>/queue/independent_access_ranges/ 373 |-- 0 374 | |-- nr_sectors 375 | `-- sector 376 `-- 1 377 |-- nr_sectors 378 `-- sector 379 380 The sector and nr_sectors attributes use 512B sector unit, 381 regardless of the actual block size of the device. Independent 382 access ranges do not overlap and include all sectors within the 383 device capacity. The access ranges are numbered in increasing 384 order of the range start sector, that is, the sector attribute 385 of range 0 always has the value 0. 386 387 388What: /sys/block/<disk>/queue/io_poll 389Date: November 2015 390Contact: linux-block@vger.kernel.org 391Description: 392 [RW] When read, this file shows whether polling is enabled (1) 393 or disabled (0). Writing '0' to this file will disable polling 394 for this device. Writing any non-zero value will enable this 395 feature. 396 397 398What: /sys/block/<disk>/queue/io_poll_delay 399Date: November 2016 400Contact: linux-block@vger.kernel.org 401Description: 402 [RW] This was used to control what kind of polling will be 403 performed. It is now fixed to -1, which is classic polling. 404 In this mode, the CPU will repeatedly ask for completions 405 without giving up any time. 406 <deprecated> 407 408 409What: /sys/block/<disk>/queue/io_timeout 410Date: November 2018 411Contact: Weiping Zhang <zhangweiping@didiglobal.com> 412Description: 413 [RW] io_timeout is the request timeout in milliseconds. If a 414 request does not complete in this time then the block driver 415 timeout handler is invoked. That timeout handler can decide to 416 retry the request, to fail it or to start a device recovery 417 strategy. 418 419 420What: /sys/block/<disk>/queue/iostats 421Date: January 2009 422Contact: linux-block@vger.kernel.org 423Description: 424 [RW] This file is used to control (on/off) the iostats 425 accounting of the disk. 426 427 428What: /sys/block/<disk>/queue/logical_block_size 429Date: May 2009 430Contact: Martin K. Petersen <martin.petersen@oracle.com> 431Description: 432 [RO] This is the smallest unit the storage device can address. 433 It is typically 512 bytes. 434 435 436What: /sys/block/<disk>/queue/max_active_zones 437Date: July 2020 438Contact: Niklas Cassel <niklas.cassel@wdc.com> 439Description: 440 [RO] For zoned block devices (zoned attribute indicating 441 "host-managed" or "host-aware"), the sum of zones belonging to 442 any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED, 443 is limited by this value. If this value is 0, there is no limit. 444 445 If the host attempts to exceed this limit, the driver should 446 report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user 447 space may see as the EOVERFLOW errno. 448 449 450What: /sys/block/<disk>/queue/max_discard_segments 451Date: February 2017 452Contact: linux-block@vger.kernel.org 453Description: 454 [RO] The maximum number of DMA scatter/gather entries in a 455 discard request. 456 457 458What: /sys/block/<disk>/queue/max_hw_sectors_kb 459Date: September 2004 460Contact: linux-block@vger.kernel.org 461Description: 462 [RO] This is the maximum number of kilobytes supported in a 463 single data transfer. 464 465 466What: /sys/block/<disk>/queue/max_integrity_segments 467Date: September 2010 468Contact: linux-block@vger.kernel.org 469Description: 470 [RO] Maximum number of elements in a DMA scatter/gather list 471 with integrity data that will be submitted by the block layer 472 core to the associated block driver. 473 474 475What: /sys/block/<disk>/queue/max_open_zones 476Date: July 2020 477Contact: Niklas Cassel <niklas.cassel@wdc.com> 478Description: 479 [RO] For zoned block devices (zoned attribute indicating 480 "host-managed" or "host-aware"), the sum of zones belonging to 481 any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is 482 limited by this value. If this value is 0, there is no limit. 483 484 485What: /sys/block/<disk>/queue/max_sectors_kb 486Date: September 2004 487Contact: linux-block@vger.kernel.org 488Description: 489 [RW] This is the maximum number of kilobytes that the block 490 layer will allow for a filesystem request. Must be smaller than 491 or equal to the maximum size allowed by the hardware. Write 0 492 to use default kernel settings. 493 494 495What: /sys/block/<disk>/queue/max_segment_size 496Date: March 2010 497Contact: linux-block@vger.kernel.org 498Description: 499 [RO] Maximum size in bytes of a single element in a DMA 500 scatter/gather list. 501 502 503What: /sys/block/<disk>/queue/max_segments 504Date: March 2010 505Contact: linux-block@vger.kernel.org 506Description: 507 [RO] Maximum number of elements in a DMA scatter/gather list 508 that is submitted to the associated block driver. 509 510 511What: /sys/block/<disk>/queue/minimum_io_size 512Date: April 2009 513Contact: Martin K. Petersen <martin.petersen@oracle.com> 514Description: 515 [RO] Storage devices may report a granularity or preferred 516 minimum I/O size which is the smallest request the device can 517 perform without incurring a performance penalty. For disk 518 drives this is often the physical block size. For RAID arrays 519 it is often the stripe chunk size. A properly aligned multiple 520 of minimum_io_size is the preferred request size for workloads 521 where a high number of I/O operations is desired. 522 523 524What: /sys/block/<disk>/queue/nomerges 525Date: January 2010 526Contact: linux-block@vger.kernel.org 527Description: 528 [RW] Standard I/O elevator operations include attempts to merge 529 contiguous I/Os. For known random I/O loads these attempts will 530 always fail and result in extra cycles being spent in the 531 kernel. This allows one to turn off this behavior on one of two 532 ways: When set to 1, complex merge checks are disabled, but the 533 simple one-shot merges with the previous I/O request are 534 enabled. When set to 2, all merge tries are disabled. The 535 default value is 0 - which enables all types of merge tries. 536 537 538What: /sys/block/<disk>/queue/nr_requests 539Date: July 2003 540Contact: linux-block@vger.kernel.org 541Description: 542 [RW] This controls how many requests may be allocated in the 543 block layer for read or write requests. Note that the total 544 allocated number may be twice this amount, since it applies only 545 to reads or writes (not the accumulated sum). 546 547 To avoid priority inversion through request starvation, a 548 request queue maintains a separate request pool per each cgroup 549 when CONFIG_BLK_CGROUP is enabled, and this parameter applies to 550 each such per-block-cgroup request pool. IOW, if there are N 551 block cgroups, each request queue may have up to N request 552 pools, each independently regulated by nr_requests. 553 554 555What: /sys/block/<disk>/queue/nr_zones 556Date: November 2018 557Contact: Damien Le Moal <damien.lemoal@wdc.com> 558Description: 559 [RO] nr_zones indicates the total number of zones of a zoned 560 block device ("host-aware" or "host-managed" zone model). For 561 regular block devices, the value is always 0. 562 563 564What: /sys/block/<disk>/queue/optimal_io_size 565Date: April 2009 566Contact: Martin K. Petersen <martin.petersen@oracle.com> 567Description: 568 [RO] Storage devices may report an optimal I/O size, which is 569 the device's preferred unit for sustained I/O. This is rarely 570 reported for disk drives. For RAID arrays it is usually the 571 stripe width or the internal track size. A properly aligned 572 multiple of optimal_io_size is the preferred request size for 573 workloads where sustained throughput is desired. If no optimal 574 I/O size is reported this file contains 0. 575 576 577What: /sys/block/<disk>/queue/physical_block_size 578Date: May 2009 579Contact: Martin K. Petersen <martin.petersen@oracle.com> 580Description: 581 [RO] This is the smallest unit a physical storage device can 582 write atomically. It is usually the same as the logical block 583 size but may be bigger. One example is SATA drives with 4KB 584 sectors that expose a 512-byte logical block size to the 585 operating system. For stacked block devices the 586 physical_block_size variable contains the maximum 587 physical_block_size of the component devices. 588 589 590What: /sys/block/<disk>/queue/read_ahead_kb 591Date: May 2004 592Contact: linux-block@vger.kernel.org 593Description: 594 [RW] Maximum number of kilobytes to read-ahead for filesystems 595 on this block device. 596 597 598What: /sys/block/<disk>/queue/rotational 599Date: January 2009 600Contact: linux-block@vger.kernel.org 601Description: 602 [RW] This file is used to stat if the device is of rotational 603 type or non-rotational type. 604 605 606What: /sys/block/<disk>/queue/rq_affinity 607Date: September 2008 608Contact: linux-block@vger.kernel.org 609Description: 610 [RW] If this option is '1', the block layer will migrate request 611 completions to the cpu "group" that originally submitted the 612 request. For some workloads this provides a significant 613 reduction in CPU cycles due to caching effects. 614 615 For storage configurations that need to maximize distribution of 616 completion processing setting this option to '2' forces the 617 completion to run on the requesting cpu (bypassing the "group" 618 aggregation logic). 619 620 621What: /sys/block/<disk>/queue/scheduler 622Date: October 2004 623Contact: linux-block@vger.kernel.org 624Description: 625 [RW] When read, this file will display the current and available 626 IO schedulers for this block device. The currently active IO 627 scheduler will be enclosed in [] brackets. Writing an IO 628 scheduler name to this file will switch control of this block 629 device to that new IO scheduler. Note that writing an IO 630 scheduler name to this file will attempt to load that IO 631 scheduler module, if it isn't already present in the system. 632 633 634What: /sys/block/<disk>/queue/stable_writes 635Date: September 2020 636Contact: linux-block@vger.kernel.org 637Description: 638 [RW] This file will contain '1' if memory must not be modified 639 while it is being used in a write request to this device. When 640 this is the case and the kernel is performing writeback of a 641 page, the kernel will wait for writeback to complete before 642 allowing the page to be modified again, rather than allowing 643 immediate modification as is normally the case. This 644 restriction arises when the device accesses the memory multiple 645 times where the same data must be seen every time -- for 646 example, once to calculate a checksum and once to actually write 647 the data. If no such restriction exists, this file will contain 648 '0'. This file is writable for testing purposes. 649 650What: /sys/block/<disk>/queue/virt_boundary_mask 651Date: April 2021 652Contact: linux-block@vger.kernel.org 653Description: 654 [RO] This file shows the I/O segment memory alignment mask for 655 the block device. I/O requests to this device will be split 656 between segments wherever either the memory address of the end 657 of the previous segment or the memory address of the beginning 658 of the current segment is not aligned to virt_boundary_mask + 1 659 bytes. 660 661 662What: /sys/block/<disk>/queue/wbt_lat_usec 663Date: November 2016 664Contact: linux-block@vger.kernel.org 665Description: 666 [RW] If the device is registered for writeback throttling, then 667 this file shows the target minimum read latency. If this latency 668 is exceeded in a given window of time (see wb_window_usec), then 669 the writeback throttling will start scaling back writes. Writing 670 a value of '0' to this file disables the feature. Writing a 671 value of '-1' to this file resets the value to the default 672 setting. 673 674 675What: /sys/block/<disk>/queue/write_cache 676Date: April 2016 677Contact: linux-block@vger.kernel.org 678Description: 679 [RW] When read, this file will display whether the device has 680 write back caching enabled or not. It will return "write back" 681 for the former case, and "write through" for the latter. Writing 682 to this file can change the kernels view of the device, but it 683 doesn't alter the device state. This means that it might not be 684 safe to toggle the setting from "write back" to "write through", 685 since that will also eliminate cache flushes issued by the 686 kernel. 687 688 689What: /sys/block/<disk>/queue/write_same_max_bytes 690Date: January 2012 691Contact: Martin K. Petersen <martin.petersen@oracle.com> 692Description: 693 [RO] Some devices support a write same operation in which a 694 single data block can be written to a range of several 695 contiguous blocks on storage. This can be used to wipe areas on 696 disk or to initialize drives in a RAID configuration. 697 write_same_max_bytes indicates how many bytes can be written in 698 a single write same command. If write_same_max_bytes is 0, write 699 same is not supported by the device. 700 701 702What: /sys/block/<disk>/queue/write_zeroes_max_bytes 703Date: November 2016 704Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> 705Description: 706 [RO] Devices that support write zeroes operation in which a 707 single request can be issued to zero out the range of contiguous 708 blocks on storage without having any payload in the request. 709 This can be used to optimize writing zeroes to the devices. 710 write_zeroes_max_bytes indicates how many bytes can be written 711 in a single write zeroes command. If write_zeroes_max_bytes is 712 0, write zeroes is not supported by the device. 713 714 715What: /sys/block/<disk>/queue/zone_append_max_bytes 716Date: May 2020 717Contact: linux-block@vger.kernel.org 718Description: 719 [RO] This is the maximum number of bytes that can be written to 720 a sequential zone of a zoned block device using a zone append 721 write operation (REQ_OP_ZONE_APPEND). This value is always 0 for 722 regular block devices. 723 724 725What: /sys/block/<disk>/queue/zone_write_granularity 726Date: January 2021 727Contact: linux-block@vger.kernel.org 728Description: 729 [RO] This indicates the alignment constraint, in bytes, for 730 write operations in sequential zones of zoned block devices 731 (devices with a zoned attributed that reports "host-managed" or 732 "host-aware"). This value is always 0 for regular block devices. 733 734 735What: /sys/block/<disk>/queue/zoned 736Date: September 2016 737Contact: Damien Le Moal <damien.lemoal@wdc.com> 738Description: 739 [RO] zoned indicates if the device is a zoned block device and 740 the zone model of the device if it is indeed zoned. The 741 possible values indicated by zoned are "none" for regular block 742 devices and "host-aware" or "host-managed" for zoned block 743 devices. The characteristics of host-aware and host-managed 744 zoned block devices are described in the ZBC (Zoned Block 745 Commands) and ZAC (Zoned Device ATA Command Set) standards. 746 These standards also define the "drive-managed" zone model. 747 However, since drive-managed zoned block devices do not support 748 zone commands, they will be treated as regular block devices and 749 zoned will report "none". 750 751 752What: /sys/block/<disk>/hidden 753Date: March 2023 754Contact: linux-block@vger.kernel.org 755Description: 756 [RO] the block device is hidden. it doesn’t produce events, and 757 can’t be opened from userspace or using blkdev_get*. 758 Used for the underlying components of multipath devices. 759 760 761What: /sys/block/<disk>/stat 762Date: February 2008 763Contact: Jerome Marchand <jmarchan@redhat.com> 764Description: 765 The /sys/block/<disk>/stat files displays the I/O 766 statistics of disk <disk>. They contain 11 fields: 767 768 == ============================================== 769 1 reads completed successfully 770 2 reads merged 771 3 sectors read 772 4 time spent reading (ms) 773 5 writes completed 774 6 writes merged 775 7 sectors written 776 8 time spent writing (ms) 777 9 I/Os currently in progress 778 10 time spent doing I/Os (ms) 779 11 weighted time spent doing I/Os (ms) 780 12 discards completed 781 13 discards merged 782 14 sectors discarded 783 15 time spent discarding (ms) 784 16 flush requests completed 785 17 time spent flushing (ms) 786 == ============================================== 787 788 For more details refer Documentation/admin-guide/iostats.rst 789