1 What: /sys/block/<disk>/alignment_offset
2 Date: April 2009
3 Contact: Martin K. Petersen <martin.petersen@oracle.com>
4 Description:
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
13 What: /sys/block/<disk>/discard_alignment
14 Date: May 2011
15 Contact: Martin K. Petersen <martin.petersen@oracle.com>
16 Description:
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
24 What: /sys/block/<disk>/atomic_write_max_bytes
25 Date: February 2024
26 Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
27 Description:
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
42 What: /sys/block/<disk>/atomic_write_unit_min_bytes
43 Date: February 2024
44 Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
45 Description:
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
53 What: /sys/block/<disk>/atomic_write_unit_max_bytes
54 Date: February 2024
55 Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
56 Description:
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
64 What: /sys/block/<disk>/atomic_write_boundary_bytes
65 Date: February 2024
66 Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
67 Description:
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
78 What: /sys/block/<disk>/diskseq
79 Date: February 2021
80 Contact: Matteo Croce <mcroce@microsoft.com>
81 Description:
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
90 What: /sys/block/<disk>/inflight
91 Date: October 2009
92 Contact: Jens Axboe <axboe@kernel.dk>, Nikanth Karthikesan <knikanth@suse.de>
93 Description:
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
106 What: /sys/block/<disk>/integrity/device_is_integrity_capable
107 Date: July 2014
108 Contact: Martin K. Petersen <martin.petersen@oracle.com>
109 Description:
110 Indicates whether a storage device is capable of storing
111 integrity metadata. Set if the device is T10 PI-capable.
112
113
114 What: /sys/block/<disk>/integrity/format
115 Date: June 2008
116 Contact: Martin K. Petersen <martin.petersen@oracle.com>
117 Description:
118 Metadata format for integrity capable block device.
119 E.g. T10-DIF-TYPE1-CRC.
120
121
122 What: /sys/block/<disk>/integrity/protection_interval_bytes
123 Date: July 2015
124 Contact: Martin K. Petersen <martin.petersen@oracle.com>
125 Description:
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
131 What: /sys/block/<disk>/integrity/read_verify
132 Date: June 2008
133 Contact: Martin K. Petersen <martin.petersen@oracle.com>
134 Description:
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
140 What: /sys/block/<disk>/integrity/tag_size
141 Date: June 2008
142 Contact: Martin K. Petersen <martin.petersen@oracle.com>
143 Description:
144 Number of bytes of integrity tag space available per
145 512 bytes of data.
146
147
148 What: /sys/block/<disk>/integrity/write_generate
149 Date: June 2008
150 Contact: Martin K. Petersen <martin.petersen@oracle.com>
151 Description:
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
157 What: /sys/block/<disk>/partscan
158 Date: May 2024
159 Contact: Christoph Hellwig <hch@lst.de>
160 Description:
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
167 What: /sys/block/<disk>/<partition>/alignment_offset
168 Date: April 2009
169 Contact: Martin K. Petersen <martin.petersen@oracle.com>
170 Description:
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
179 What: /sys/block/<disk>/<partition>/discard_alignment
180 Date: May 2011
181 Contact: Martin K. Petersen <martin.petersen@oracle.com>
182 Description:
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
191 What: /sys/block/<disk>/<partition>/stat
192 Date: February 2008
193 Contact: Jerome Marchand <jmarchan@redhat.com>
194 Description:
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
200 What: /sys/block/<disk>/queue/add_random
201 Date: June 2010
202 Contact: linux-block@vger.kernel.org
203 Description:
204 [RW] This file allows to turn off the disk entropy contribution.
205 Default value of this file is '1'(on).
206
207
208 What: /sys/block/<disk>/queue/chunk_sectors
209 Date: September 2016
210 Contact: Hannes Reinecke <hare@suse.com>
211 Description:
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
221 What: /sys/block/<disk>/queue/crypto/
222 Date: February 2022
223 Contact: linux-block@vger.kernel.org
224 Description:
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
232 What: /sys/block/<disk>/queue/crypto/max_dun_bits
233 Date: February 2022
234 Contact: linux-block@vger.kernel.org
235 Description:
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
240 What: /sys/block/<disk>/queue/crypto/modes/<mode>
241 Date: February 2022
242 Contact: linux-block@vger.kernel.org
243 Description:
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
262 What: /sys/block/<disk>/queue/crypto/num_keyslots
263 Date: February 2022
264 Contact: linux-block@vger.kernel.org
265 Description:
266 [RO] This file shows the number of keyslots the device has for
267 use with inline encryption.
268
269
270 What: /sys/block/<disk>/queue/dax
271 Date: June 2016
272 Contact: linux-block@vger.kernel.org
273 Description:
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
279 What: /sys/block/<disk>/queue/discard_granularity
280 Date: May 2011
281 Contact: Martin K. Petersen <martin.petersen@oracle.com>
282 Description:
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
292 What: /sys/block/<disk>/queue/discard_max_bytes
293 Date: May 2011
294 Contact: Martin K. Petersen <martin.petersen@oracle.com>
295 Description:
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
304 What: /sys/block/<disk>/queue/discard_max_hw_bytes
305 Date: July 2015
306 Contact: linux-block@vger.kernel.org
307 Description:
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
318 What: /sys/block/<disk>/queue/discard_zeroes_data
319 Date: May 2011
320 Contact: Martin K. Petersen <martin.petersen@oracle.com>
321 Description:
322 [RO] Will always return 0. Don't rely on any specific behavior
323 for discards, and don't read this file.
324
325
326 What: /sys/block/<disk>/queue/dma_alignment
327 Date: May 2022
328 Contact: linux-block@vger.kernel.org
329 Description:
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
335 What: /sys/block/<disk>/queue/fua
336 Date: May 2018
337 Contact: linux-block@vger.kernel.org
338 Description:
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
345 What: /sys/block/<disk>/queue/hw_sector_size
346 Date: January 2008
347 Contact: linux-block@vger.kernel.org
348 Description:
349 [RO] This is the hardware sector size of the device, in bytes.
350
351
352 What: /sys/block/<disk>/queue/independent_access_ranges/
353 Date: October 2021
354 Contact: linux-block@vger.kernel.org
355 Description:
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
388 What: /sys/block/<disk>/queue/io_poll
389 Date: November 2015
390 Contact: linux-block@vger.kernel.org
391 Description:
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
398 What: /sys/block/<disk>/queue/io_poll_delay
399 Date: November 2016
400 Contact: linux-block@vger.kernel.org
401 Description:
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
409 What: /sys/block/<disk>/queue/io_timeout
410 Date: November 2018
411 Contact: Weiping Zhang <zhangweiping@didiglobal.com>
412 Description:
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
420 What: /sys/block/<disk>/queue/iostats
421 Date: January 2009
422 Contact: linux-block@vger.kernel.org
423 Description:
424 [RW] This file is used to control (on/off) the iostats
425 accounting of the disk.
426
427
428 What: /sys/block/<disk>/queue/logical_block_size
429 Date: May 2009
430 Contact: Martin K. Petersen <martin.petersen@oracle.com>
431 Description:
432 [RO] This is the smallest unit the storage device can address.
433 It is typically 512 bytes.
434
435
436 What: /sys/block/<disk>/queue/max_active_zones
437 Date: July 2020
438 Contact: Niklas Cassel <niklas.cassel@wdc.com>
439 Description:
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
450 What: /sys/block/<disk>/queue/max_discard_segments
451 Date: February 2017
452 Contact: linux-block@vger.kernel.org
453 Description:
454 [RO] The maximum number of DMA scatter/gather entries in a
455 discard request.
456
457
458 What: /sys/block/<disk>/queue/max_hw_sectors_kb
459 Date: September 2004
460 Contact: linux-block@vger.kernel.org
461 Description:
462 [RO] This is the maximum number of kilobytes supported in a
463 single data transfer.
464
465
466 What: /sys/block/<disk>/queue/max_integrity_segments
467 Date: September 2010
468 Contact: linux-block@vger.kernel.org
469 Description:
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
475 What: /sys/block/<disk>/queue/max_open_zones
476 Date: July 2020
477 Contact: Niklas Cassel <niklas.cassel@wdc.com>
478 Description:
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
485 What: /sys/block/<disk>/queue/max_sectors_kb
486 Date: September 2004
487 Contact: linux-block@vger.kernel.org
488 Description:
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
495 What: /sys/block/<disk>/queue/max_segment_size
496 Date: March 2010
497 Contact: linux-block@vger.kernel.org
498 Description:
499 [RO] Maximum size in bytes of a single element in a DMA
500 scatter/gather list.
501
502
503 What: /sys/block/<disk>/queue/max_segments
504 Date: March 2010
505 Contact: linux-block@vger.kernel.org
506 Description:
507 [RO] Maximum number of elements in a DMA scatter/gather list
508 that is submitted to the associated block driver.
509
510
511 What: /sys/block/<disk>/queue/minimum_io_size
512 Date: April 2009
513 Contact: Martin K. Petersen <martin.petersen@oracle.com>
514 Description:
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
524 What: /sys/block/<disk>/queue/nomerges
525 Date: January 2010
526 Contact: linux-block@vger.kernel.org
527 Description:
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
538 What: /sys/block/<disk>/queue/nr_requests
539 Date: July 2003
540 Contact: linux-block@vger.kernel.org
541 Description:
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
555 What: /sys/block/<disk>/queue/nr_zones
556 Date: November 2018
557 Contact: Damien Le Moal <damien.lemoal@wdc.com>
558 Description:
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
564 What: /sys/block/<disk>/queue/optimal_io_size
565 Date: April 2009
566 Contact: Martin K. Petersen <martin.petersen@oracle.com>
567 Description:
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
577 What: /sys/block/<disk>/queue/physical_block_size
578 Date: May 2009
579 Contact: Martin K. Petersen <martin.petersen@oracle.com>
580 Description:
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
590 What: /sys/block/<disk>/queue/read_ahead_kb
591 Date: May 2004
592 Contact: linux-block@vger.kernel.org
593 Description:
594 [RW] Maximum number of kilobytes to read-ahead for filesystems
595 on this block device.
596
597
598 What: /sys/block/<disk>/queue/rotational
599 Date: January 2009
600 Contact: linux-block@vger.kernel.org
601 Description:
602 [RW] This file is used to stat if the device is of rotational
603 type or non-rotational type.
604
605
606 What: /sys/block/<disk>/queue/rq_affinity
607 Date: September 2008
608 Contact: linux-block@vger.kernel.org
609 Description:
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
621 What: /sys/block/<disk>/queue/scheduler
622 Date: October 2004
623 Contact: linux-block@vger.kernel.org
624 Description:
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
634 What: /sys/block/<disk>/queue/stable_writes
635 Date: September 2020
636 Contact: linux-block@vger.kernel.org
637 Description:
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
650 What: /sys/block/<disk>/queue/virt_boundary_mask
651 Date: April 2021
652 Contact: linux-block@vger.kernel.org
653 Description:
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
662 What: /sys/block/<disk>/queue/wbt_lat_usec
663 Date: November 2016
664 Contact: linux-block@vger.kernel.org
665 Description:
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
675 What: /sys/block/<disk>/queue/write_cache
676 Date: April 2016
677 Contact: linux-block@vger.kernel.org
678 Description:
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
689 What: /sys/block/<disk>/queue/write_same_max_bytes
690 Date: January 2012
691 Contact: Martin K. Petersen <martin.petersen@oracle.com>
692 Description:
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
702 What: /sys/block/<disk>/queue/write_zeroes_max_bytes
703 Date: November 2016
704 Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
705 Description:
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
715 What: /sys/block/<disk>/queue/zone_append_max_bytes
716 Date: May 2020
717 Contact: linux-block@vger.kernel.org
718 Description:
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
725 What: /sys/block/<disk>/queue/zone_write_granularity
726 Date: January 2021
727 Contact: linux-block@vger.kernel.org
728 Description:
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
735 What: /sys/block/<disk>/queue/zoned
736 Date: September 2016
737 Contact: Damien Le Moal <damien.lemoal@wdc.com>
738 Description:
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
752 What: /sys/block/<disk>/hidden
753 Date: March 2023
754 Contact: linux-block@vger.kernel.org
755 Description:
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
761 What: /sys/block/<disk>/stat
762 Date: February 2008
763 Contact: Jerome Marchand <jmarchan@redhat.com>
764 Description:
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
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