1 What: /sys/block/<disk>/alignment_offset
3 Contact: Martin K. Petersen <martin.petersen@oracle.com>
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.
13 What: /sys/block/<disk>/discard_alignment
15 Contact: Martin K. Petersen <martin.petersen@oracle.com>
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
25 What: /sys/block/<disk>/diskseq
27 Contact: Matteo Croce <mcroce@microsoft.com>
29 The /sys/block/<disk>/diskseq files reports the disk
30 sequence number, which is a monotonically increasing
31 number assigned to every drive.
32 Some devices, like the loop device, refresh such number
33 every time the backing file is changed.
34 The value type is 64 bit unsigned.
37 What: /sys/block/<disk>/inflight
39 Contact: Jens Axboe <axboe@kernel.dk>, Nikanth Karthikesan <knikanth@suse.de>
41 Reports the number of I/O requests currently in progress
42 (pending / in flight) in a device driver. This can be less
43 than the number of requests queued in the block device queue.
44 The report contains 2 fields: one for read requests
45 and one for write requests.
46 The value type is unsigned int.
47 Cf. Documentation/block/stat.rst which contains a single value for
49 This is related to /sys/block/<disk>/queue/nr_requests
50 and for SCSI device also its queue_depth.
53 What: /sys/block/<disk>/integrity/device_is_integrity_capable
55 Contact: Martin K. Petersen <martin.petersen@oracle.com>
57 Indicates whether a storage device is capable of storing
58 integrity metadata. Set if the device is T10 PI-capable.
61 What: /sys/block/<disk>/integrity/format
63 Contact: Martin K. Petersen <martin.petersen@oracle.com>
65 Metadata format for integrity capable block device.
66 E.g. T10-DIF-TYPE1-CRC.
69 What: /sys/block/<disk>/integrity/protection_interval_bytes
71 Contact: Martin K. Petersen <martin.petersen@oracle.com>
73 Describes the number of data bytes which are protected
74 by one integrity tuple. Typically the device's logical
78 What: /sys/block/<disk>/integrity/read_verify
80 Contact: Martin K. Petersen <martin.petersen@oracle.com>
82 Indicates whether the block layer should verify the
83 integrity of read requests serviced by devices that
84 support sending integrity metadata.
87 What: /sys/block/<disk>/integrity/tag_size
89 Contact: Martin K. Petersen <martin.petersen@oracle.com>
91 Number of bytes of integrity tag space available per
95 What: /sys/block/<disk>/integrity/write_generate
97 Contact: Martin K. Petersen <martin.petersen@oracle.com>
99 Indicates whether the block layer should automatically
100 generate checksums for write requests bound for
101 devices that support receiving integrity metadata.
104 What: /sys/block/<disk>/<partition>/alignment_offset
106 Contact: Martin K. Petersen <martin.petersen@oracle.com>
108 Storage devices may report a physical block size that is
109 bigger than the logical block size (for instance a drive
110 with 4KB physical sectors exposing 512-byte logical
111 blocks to the operating system). This parameter
112 indicates how many bytes the beginning of the partition
113 is offset from the disk's natural alignment.
116 What: /sys/block/<disk>/<partition>/discard_alignment
118 Contact: Martin K. Petersen <martin.petersen@oracle.com>
120 Devices that support discard functionality may
121 internally allocate space in units that are bigger than
122 the exported logical block size. The discard_alignment
123 parameter indicates how many bytes the beginning of the
124 partition is offset from the internal allocation unit's
128 What: /sys/block/<disk>/<partition>/stat
130 Contact: Jerome Marchand <jmarchan@redhat.com>
132 The /sys/block/<disk>/<partition>/stat files display the
133 I/O statistics of partition <partition>. The format is the
134 same as the format of /sys/block/<disk>/stat.
137 What: /sys/block/<disk>/queue/add_random
139 Contact: linux-block@vger.kernel.org
141 [RW] This file allows to turn off the disk entropy contribution.
142 Default value of this file is '1'(on).
145 What: /sys/block/<disk>/queue/chunk_sectors
147 Contact: Hannes Reinecke <hare@suse.com>
149 [RO] chunk_sectors has different meaning depending on the type
150 of the disk. For a RAID device (dm-raid), chunk_sectors
151 indicates the size in 512B sectors of the RAID volume stripe
152 segment. For a zoned block device, either host-aware or
153 host-managed, chunk_sectors indicates the size in 512B sectors
154 of the zones of the device, with the eventual exception of the
155 last zone of the device which may be smaller.
158 What: /sys/block/<disk>/queue/crypto/
160 Contact: linux-block@vger.kernel.org
162 The presence of this subdirectory of /sys/block/<disk>/queue/
163 indicates that the device supports inline encryption. This
164 subdirectory contains files which describe the inline encryption
165 capabilities of the device. For more information about inline
166 encryption, refer to Documentation/block/inline-encryption.rst.
169 What: /sys/block/<disk>/queue/crypto/max_dun_bits
171 Contact: linux-block@vger.kernel.org
173 [RO] This file shows the maximum length, in bits, of data unit
174 numbers accepted by the device in inline encryption requests.
177 What: /sys/block/<disk>/queue/crypto/modes/<mode>
179 Contact: linux-block@vger.kernel.org
181 [RO] For each crypto mode (i.e., encryption/decryption
182 algorithm) the device supports with inline encryption, a file
183 will exist at this location. It will contain a hexadecimal
184 number that is a bitmask of the supported data unit sizes, in
185 bytes, for that crypto mode.
187 Currently, the crypto modes that may be supported are:
193 For example, if a device supports AES-256-XTS inline encryption
194 with data unit sizes of 512 and 4096 bytes, the file
195 /sys/block/<disk>/queue/crypto/modes/AES-256-XTS will exist and
196 will contain "0x1200".
199 What: /sys/block/<disk>/queue/crypto/num_keyslots
201 Contact: linux-block@vger.kernel.org
203 [RO] This file shows the number of keyslots the device has for
204 use with inline encryption.
207 What: /sys/block/<disk>/queue/dax
209 Contact: linux-block@vger.kernel.org
211 [RO] This file indicates whether the device supports Direct
212 Access (DAX), used by CPU-addressable storage to bypass the
213 pagecache. It shows '1' if true, '0' if not.
216 What: /sys/block/<disk>/queue/discard_granularity
218 Contact: Martin K. Petersen <martin.petersen@oracle.com>
220 [RO] Devices that support discard functionality may internally
221 allocate space using units that are bigger than the logical
222 block size. The discard_granularity parameter indicates the size
223 of the internal allocation unit in bytes if reported by the
224 device. Otherwise the discard_granularity will be set to match
225 the device's physical block size. A discard_granularity of 0
226 means that the device does not support discard functionality.
229 What: /sys/block/<disk>/queue/discard_max_bytes
231 Contact: Martin K. Petersen <martin.petersen@oracle.com>
233 [RW] While discard_max_hw_bytes is the hardware limit for the
234 device, this setting is the software limit. Some devices exhibit
235 large latencies when large discards are issued, setting this
236 value lower will make Linux issue smaller discards and
237 potentially help reduce latencies induced by large discard
241 What: /sys/block/<disk>/queue/discard_max_hw_bytes
243 Contact: linux-block@vger.kernel.org
245 [RO] Devices that support discard functionality may have
246 internal limits on the number of bytes that can be trimmed or
247 unmapped in a single operation. The `discard_max_hw_bytes`
248 parameter is set by the device driver to the maximum number of
249 bytes that can be discarded in a single operation. Discard
250 requests issued to the device must not exceed this limit. A
251 `discard_max_hw_bytes` value of 0 means that the device does not
252 support discard functionality.
255 What: /sys/block/<disk>/queue/discard_zeroes_data
257 Contact: Martin K. Petersen <martin.petersen@oracle.com>
259 [RO] Will always return 0. Don't rely on any specific behavior
260 for discards, and don't read this file.
263 What: /sys/block/<disk>/queue/dma_alignment
265 Contact: linux-block@vger.kernel.org
267 Reports the alignment that user space addresses must have to be
268 used for raw block device access with O_DIRECT and other driver
269 specific passthrough mechanisms.
272 What: /sys/block/<disk>/queue/fua
274 Contact: linux-block@vger.kernel.org
276 [RO] Whether or not the block driver supports the FUA flag for
277 write requests. FUA stands for Force Unit Access. If the FUA
278 flag is set that means that write requests must bypass the
279 volatile cache of the storage device.
282 What: /sys/block/<disk>/queue/hw_sector_size
284 Contact: linux-block@vger.kernel.org
286 [RO] This is the hardware sector size of the device, in bytes.
289 What: /sys/block/<disk>/queue/independent_access_ranges/
291 Contact: linux-block@vger.kernel.org
293 [RO] The presence of this sub-directory of the
294 /sys/block/xxx/queue/ directory indicates that the device is
295 capable of executing requests targeting different sector ranges
296 in parallel. For instance, single LUN multi-actuator hard-disks
297 will have an independent_access_ranges directory if the device
298 correctly advertizes the sector ranges of its actuators.
300 The independent_access_ranges directory contains one directory
301 per access range, with each range described using the sector
302 (RO) attribute file to indicate the first sector of the range
303 and the nr_sectors (RO) attribute file to indicate the total
304 number of sectors in the range starting from the first sector of
305 the range. For example, a dual-actuator hard-disk will have the
306 following independent_access_ranges entries.::
308 $ tree /sys/block/<disk>/queue/independent_access_ranges/
309 /sys/block/<disk>/queue/independent_access_ranges/
317 The sector and nr_sectors attributes use 512B sector unit,
318 regardless of the actual block size of the device. Independent
319 access ranges do not overlap and include all sectors within the
320 device capacity. The access ranges are numbered in increasing
321 order of the range start sector, that is, the sector attribute
322 of range 0 always has the value 0.
325 What: /sys/block/<disk>/queue/io_poll
327 Contact: linux-block@vger.kernel.org
329 [RW] When read, this file shows whether polling is enabled (1)
330 or disabled (0). Writing '0' to this file will disable polling
331 for this device. Writing any non-zero value will enable this
335 What: /sys/block/<disk>/queue/io_poll_delay
337 Contact: linux-block@vger.kernel.org
339 [RW] If polling is enabled, this controls what kind of polling
340 will be performed. It defaults to -1, which is classic polling.
341 In this mode, the CPU will repeatedly ask for completions
342 without giving up any time. If set to 0, a hybrid polling mode
343 is used, where the kernel will attempt to make an educated guess
344 at when the IO will complete. Based on this guess, the kernel
345 will put the process issuing IO to sleep for an amount of time,
346 before entering a classic poll loop. This mode might be a little
347 slower than pure classic polling, but it will be more efficient.
348 If set to a value larger than 0, the kernel will put the process
349 issuing IO to sleep for this amount of microseconds before
350 entering classic polling.
353 What: /sys/block/<disk>/queue/io_timeout
355 Contact: Weiping Zhang <zhangweiping@didiglobal.com>
357 [RW] io_timeout is the request timeout in milliseconds. If a
358 request does not complete in this time then the block driver
359 timeout handler is invoked. That timeout handler can decide to
360 retry the request, to fail it or to start a device recovery
364 What: /sys/block/<disk>/queue/iostats
366 Contact: linux-block@vger.kernel.org
368 [RW] This file is used to control (on/off) the iostats
369 accounting of the disk.
372 What: /sys/block/<disk>/queue/logical_block_size
374 Contact: Martin K. Petersen <martin.petersen@oracle.com>
376 [RO] This is the smallest unit the storage device can address.
377 It is typically 512 bytes.
380 What: /sys/block/<disk>/queue/max_active_zones
382 Contact: Niklas Cassel <niklas.cassel@wdc.com>
384 [RO] For zoned block devices (zoned attribute indicating
385 "host-managed" or "host-aware"), the sum of zones belonging to
386 any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED,
387 is limited by this value. If this value is 0, there is no limit.
389 If the host attempts to exceed this limit, the driver should
390 report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user
391 space may see as the EOVERFLOW errno.
394 What: /sys/block/<disk>/queue/max_discard_segments
396 Contact: linux-block@vger.kernel.org
398 [RO] The maximum number of DMA scatter/gather entries in a
402 What: /sys/block/<disk>/queue/max_hw_sectors_kb
404 Contact: linux-block@vger.kernel.org
406 [RO] This is the maximum number of kilobytes supported in a
407 single data transfer.
410 What: /sys/block/<disk>/queue/max_integrity_segments
412 Contact: linux-block@vger.kernel.org
414 [RO] Maximum number of elements in a DMA scatter/gather list
415 with integrity data that will be submitted by the block layer
416 core to the associated block driver.
419 What: /sys/block/<disk>/queue/max_open_zones
421 Contact: Niklas Cassel <niklas.cassel@wdc.com>
423 [RO] For zoned block devices (zoned attribute indicating
424 "host-managed" or "host-aware"), the sum of zones belonging to
425 any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is
426 limited by this value. If this value is 0, there is no limit.
429 What: /sys/block/<disk>/queue/max_sectors_kb
431 Contact: linux-block@vger.kernel.org
433 [RW] This is the maximum number of kilobytes that the block
434 layer will allow for a filesystem request. Must be smaller than
435 or equal to the maximum size allowed by the hardware.
438 What: /sys/block/<disk>/queue/max_segment_size
440 Contact: linux-block@vger.kernel.org
442 [RO] Maximum size in bytes of a single element in a DMA
446 What: /sys/block/<disk>/queue/max_segments
448 Contact: linux-block@vger.kernel.org
450 [RO] Maximum number of elements in a DMA scatter/gather list
451 that is submitted to the associated block driver.
454 What: /sys/block/<disk>/queue/minimum_io_size
456 Contact: Martin K. Petersen <martin.petersen@oracle.com>
458 [RO] Storage devices may report a granularity or preferred
459 minimum I/O size which is the smallest request the device can
460 perform without incurring a performance penalty. For disk
461 drives this is often the physical block size. For RAID arrays
462 it is often the stripe chunk size. A properly aligned multiple
463 of minimum_io_size is the preferred request size for workloads
464 where a high number of I/O operations is desired.
467 What: /sys/block/<disk>/queue/nomerges
469 Contact: linux-block@vger.kernel.org
471 [RW] Standard I/O elevator operations include attempts to merge
472 contiguous I/Os. For known random I/O loads these attempts will
473 always fail and result in extra cycles being spent in the
474 kernel. This allows one to turn off this behavior on one of two
475 ways: When set to 1, complex merge checks are disabled, but the
476 simple one-shot merges with the previous I/O request are
477 enabled. When set to 2, all merge tries are disabled. The
478 default value is 0 - which enables all types of merge tries.
481 What: /sys/block/<disk>/queue/nr_requests
483 Contact: linux-block@vger.kernel.org
485 [RW] This controls how many requests may be allocated in the
486 block layer for read or write requests. Note that the total
487 allocated number may be twice this amount, since it applies only
488 to reads or writes (not the accumulated sum).
490 To avoid priority inversion through request starvation, a
491 request queue maintains a separate request pool per each cgroup
492 when CONFIG_BLK_CGROUP is enabled, and this parameter applies to
493 each such per-block-cgroup request pool. IOW, if there are N
494 block cgroups, each request queue may have up to N request
495 pools, each independently regulated by nr_requests.
498 What: /sys/block/<disk>/queue/nr_zones
500 Contact: Damien Le Moal <damien.lemoal@wdc.com>
502 [RO] nr_zones indicates the total number of zones of a zoned
503 block device ("host-aware" or "host-managed" zone model). For
504 regular block devices, the value is always 0.
507 What: /sys/block/<disk>/queue/optimal_io_size
509 Contact: Martin K. Petersen <martin.petersen@oracle.com>
511 [RO] Storage devices may report an optimal I/O size, which is
512 the device's preferred unit for sustained I/O. This is rarely
513 reported for disk drives. For RAID arrays it is usually the
514 stripe width or the internal track size. A properly aligned
515 multiple of optimal_io_size is the preferred request size for
516 workloads where sustained throughput is desired. If no optimal
517 I/O size is reported this file contains 0.
520 What: /sys/block/<disk>/queue/physical_block_size
522 Contact: Martin K. Petersen <martin.petersen@oracle.com>
524 [RO] This is the smallest unit a physical storage device can
525 write atomically. It is usually the same as the logical block
526 size but may be bigger. One example is SATA drives with 4KB
527 sectors that expose a 512-byte logical block size to the
528 operating system. For stacked block devices the
529 physical_block_size variable contains the maximum
530 physical_block_size of the component devices.
533 What: /sys/block/<disk>/queue/read_ahead_kb
535 Contact: linux-block@vger.kernel.org
537 [RW] Maximum number of kilobytes to read-ahead for filesystems
538 on this block device.
541 What: /sys/block/<disk>/queue/rotational
543 Contact: linux-block@vger.kernel.org
545 [RW] This file is used to stat if the device is of rotational
546 type or non-rotational type.
549 What: /sys/block/<disk>/queue/rq_affinity
551 Contact: linux-block@vger.kernel.org
553 [RW] If this option is '1', the block layer will migrate request
554 completions to the cpu "group" that originally submitted the
555 request. For some workloads this provides a significant
556 reduction in CPU cycles due to caching effects.
558 For storage configurations that need to maximize distribution of
559 completion processing setting this option to '2' forces the
560 completion to run on the requesting cpu (bypassing the "group"
564 What: /sys/block/<disk>/queue/scheduler
566 Contact: linux-block@vger.kernel.org
568 [RW] When read, this file will display the current and available
569 IO schedulers for this block device. The currently active IO
570 scheduler will be enclosed in [] brackets. Writing an IO
571 scheduler name to this file will switch control of this block
572 device to that new IO scheduler. Note that writing an IO
573 scheduler name to this file will attempt to load that IO
574 scheduler module, if it isn't already present in the system.
577 What: /sys/block/<disk>/queue/stable_writes
579 Contact: linux-block@vger.kernel.org
581 [RW] This file will contain '1' if memory must not be modified
582 while it is being used in a write request to this device. When
583 this is the case and the kernel is performing writeback of a
584 page, the kernel will wait for writeback to complete before
585 allowing the page to be modified again, rather than allowing
586 immediate modification as is normally the case. This
587 restriction arises when the device accesses the memory multiple
588 times where the same data must be seen every time -- for
589 example, once to calculate a checksum and once to actually write
590 the data. If no such restriction exists, this file will contain
591 '0'. This file is writable for testing purposes.
594 What: /sys/block/<disk>/queue/throttle_sample_time
596 Contact: linux-block@vger.kernel.org
598 [RW] This is the time window that blk-throttle samples data, in
599 millisecond. blk-throttle makes decision based on the
600 samplings. Lower time means cgroups have more smooth throughput,
601 but higher CPU overhead. This exists only when
602 CONFIG_BLK_DEV_THROTTLING_LOW is enabled.
605 What: /sys/block/<disk>/queue/virt_boundary_mask
607 Contact: linux-block@vger.kernel.org
609 [RO] This file shows the I/O segment memory alignment mask for
610 the block device. I/O requests to this device will be split
611 between segments wherever either the memory address of the end
612 of the previous segment or the memory address of the beginning
613 of the current segment is not aligned to virt_boundary_mask + 1
617 What: /sys/block/<disk>/queue/wbt_lat_usec
619 Contact: linux-block@vger.kernel.org
621 [RW] If the device is registered for writeback throttling, then
622 this file shows the target minimum read latency. If this latency
623 is exceeded in a given window of time (see wb_window_usec), then
624 the writeback throttling will start scaling back writes. Writing
625 a value of '0' to this file disables the feature. Writing a
626 value of '-1' to this file resets the value to the default
630 What: /sys/block/<disk>/queue/write_cache
632 Contact: linux-block@vger.kernel.org
634 [RW] When read, this file will display whether the device has
635 write back caching enabled or not. It will return "write back"
636 for the former case, and "write through" for the latter. Writing
637 to this file can change the kernels view of the device, but it
638 doesn't alter the device state. This means that it might not be
639 safe to toggle the setting from "write back" to "write through",
640 since that will also eliminate cache flushes issued by the
644 What: /sys/block/<disk>/queue/write_same_max_bytes
646 Contact: Martin K. Petersen <martin.petersen@oracle.com>
648 [RO] Some devices support a write same operation in which a
649 single data block can be written to a range of several
650 contiguous blocks on storage. This can be used to wipe areas on
651 disk or to initialize drives in a RAID configuration.
652 write_same_max_bytes indicates how many bytes can be written in
653 a single write same command. If write_same_max_bytes is 0, write
654 same is not supported by the device.
657 What: /sys/block/<disk>/queue/write_zeroes_max_bytes
659 Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
661 [RO] Devices that support write zeroes operation in which a
662 single request can be issued to zero out the range of contiguous
663 blocks on storage without having any payload in the request.
664 This can be used to optimize writing zeroes to the devices.
665 write_zeroes_max_bytes indicates how many bytes can be written
666 in a single write zeroes command. If write_zeroes_max_bytes is
667 0, write zeroes is not supported by the device.
670 What: /sys/block/<disk>/queue/zone_append_max_bytes
672 Contact: linux-block@vger.kernel.org
674 [RO] This is the maximum number of bytes that can be written to
675 a sequential zone of a zoned block device using a zone append
676 write operation (REQ_OP_ZONE_APPEND). This value is always 0 for
677 regular block devices.
680 What: /sys/block/<disk>/queue/zone_write_granularity
682 Contact: linux-block@vger.kernel.org
684 [RO] This indicates the alignment constraint, in bytes, for
685 write operations in sequential zones of zoned block devices
686 (devices with a zoned attributed that reports "host-managed" or
687 "host-aware"). This value is always 0 for regular block devices.
690 What: /sys/block/<disk>/queue/zoned
692 Contact: Damien Le Moal <damien.lemoal@wdc.com>
694 [RO] zoned indicates if the device is a zoned block device and
695 the zone model of the device if it is indeed zoned. The
696 possible values indicated by zoned are "none" for regular block
697 devices and "host-aware" or "host-managed" for zoned block
698 devices. The characteristics of host-aware and host-managed
699 zoned block devices are described in the ZBC (Zoned Block
700 Commands) and ZAC (Zoned Device ATA Command Set) standards.
701 These standards also define the "drive-managed" zone model.
702 However, since drive-managed zoned block devices do not support
703 zone commands, they will be treated as regular block devices and
704 zoned will report "none".
707 What: /sys/block/<disk>/stat
709 Contact: Jerome Marchand <jmarchan@redhat.com>
711 The /sys/block/<disk>/stat files displays the I/O
712 statistics of disk <disk>. They contain 11 fields:
714 == ==============================================
715 1 reads completed successfully
718 4 time spent reading (ms)
722 8 time spent writing (ms)
723 9 I/Os currently in progress
724 10 time spent doing I/Os (ms)
725 11 weighted time spent doing I/Os (ms)
726 12 discards completed
729 15 time spent discarding (ms)
730 16 flush requests completed
731 17 time spent flushing (ms)
732 == ==============================================
734 For more details refer Documentation/admin-guide/iostats.rst