public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-08-05 16:54:27 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions
linux/Documentation/ABI/stable/sysfs-block
Zhang Yi 0c40d7cb5e block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits 
Currently, disks primarily implement the write zeroes command (aka
REQ_OP_WRITE_ZEROES) through two mechanisms: the first involves
physically writing zeros to the disk media (e.g., HDDs), while the
second performs an unmap operation on the logical blocks, effectively
putting them into a deallocated state (e.g., SSDs). The first method is
generally slow, while the second method is typically very fast.

For example, on certain NVMe SSDs that support NVME_NS_DEAC, submitting
REQ_OP_WRITE_ZEROES requests with the NVME_WZ_DEAC bit can accelerate
the write zeros operation by placing disk blocks into a deallocated
state, which opportunistically avoids writing zeroes to media while
still guaranteeing that subsequent reads from the specified block range
will return zeroed data. This is a best-effort optimization, not a
mandatory requirement, some devices may partially fall back to writing
physical zeroes due to factors such as misalignment or being asked to
clear a block range smaller than the device's internal allocation unit.
Therefore, the speed of this operation is not guaranteed.

It is difficult to determine whether the storage device supports unmap
write zeroes operation. We cannot determine this by only querying
bdev_limits(bdev)->max_write_zeroes_sectors. Therefore, first, add a new
hardware queue limit parameters, max_hw_wzeroes_unmap_sectors, to
indicate whether a device supports this unmap write zeroes operation.
Then, add two new counterpart software queue limits,
max_wzeroes_unmap_sectors and max_user_wzeroes_unmap_sectors, which
allow users to disable this operation if the speed is very slow on some
sepcial devices.

Finally, for the stacked devices cases, initialize these two parameters
to UINT_MAX. This operation should be enabled by both the stacking
driver and all underlying devices.

Thanks to Martin K. Petersen for optimizing the documentation of the
write_zeroes_unmap sysfs interface.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/20250619111806.3546162-2-yi.zhang@huaweicloud.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
2025-06-23 12:45:13 +02:00

887 lines
32 KiB
Text
Raw Permalink Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

What: /sys/block/<disk>/alignment_offset
Date: April 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Storage devices may report a physical block size that is
bigger than the logical block size (for instance a drive
with 4KB physical sectors exposing 512-byte logical
blocks to the operating system). This parameter
indicates how many bytes the beginning of the device is
offset from the disk's natural alignment.
What: /sys/block/<disk>/discard_alignment
Date: May 2011
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Devices that support discard functionality may
internally allocate space in units that are bigger than
the exported logical block size. The discard_alignment
parameter indicates how many bytes the beginning of the
device is offset from the internal allocation unit's
natural alignment.
What: /sys/block/<disk>/atomic_write_max_bytes
Date: February 2024
Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
Description:
[RO] This parameter specifies the maximum atomic write
size reported by the device. This parameter is relevant
for merging of writes, where a merged atomic write
operation must not exceed this number of bytes.
This parameter may be greater than the value in
atomic_write_unit_max_bytes as
atomic_write_unit_max_bytes will be rounded down to a
power-of-two and atomic_write_unit_max_bytes may also be
limited by some other queue limits, such as max_segments.
This parameter - along with atomic_write_unit_min_bytes
and atomic_write_unit_max_bytes - will not be larger than
max_hw_sectors_kb, but may be larger than max_sectors_kb.
What: /sys/block/<disk>/atomic_write_unit_min_bytes
Date: February 2024
Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
Description:
[RO] This parameter specifies the smallest block which can
be written atomically with an atomic write operation. All
atomic write operations must begin at a
atomic_write_unit_min boundary and must be multiples of
atomic_write_unit_min. This value must be a power-of-two.
What: /sys/block/<disk>/atomic_write_unit_max_bytes
Date: February 2024
Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
Description:
[RO] This parameter defines the largest block which can be
written atomically with an atomic write operation. This
value must be a multiple of atomic_write_unit_min and must
be a power-of-two. This value will not be larger than
atomic_write_max_bytes.
What: /sys/block/<disk>/atomic_write_boundary_bytes
Date: February 2024
Contact: Himanshu Madhani <himanshu.madhani@oracle.com>
Description:
[RO] A device may need to internally split an atomic write I/O
which straddles a given logical block address boundary. This
parameter specifies the size in bytes of the atomic boundary if
one is reported by the device. This value must be a
power-of-two and at least the size as in
atomic_write_unit_max_bytes.
Any attempt to merge atomic write I/Os must not result in a
merged I/O which crosses this boundary (if any).
What: /sys/block/<disk>/diskseq
Date: February 2021
Contact: Matteo Croce <teknoraver@meta.com>
Description:
The /sys/block/<disk>/diskseq files reports the disk
sequence number, which is a monotonically increasing
number assigned to every drive.
Some devices, like the loop device, refresh such number
every time the backing file is changed.
The value type is 64 bit unsigned.
What: /sys/block/<disk>/inflight
Date: October 2009
Contact: Jens Axboe <axboe@kernel.dk>, Nikanth Karthikesan <knikanth@suse.de>
Description:
Reports the number of I/O requests currently in progress
(pending / in flight) in a device driver. This can be less
than the number of requests queued in the block device queue.
The report contains 2 fields: one for read requests
and one for write requests.
The value type is unsigned int.
Cf. Documentation/block/stat.rst which contains a single value for
requests in flight.
This is related to /sys/block/<disk>/queue/nr_requests
and for SCSI device also its queue_depth.
What: /sys/block/<disk>/integrity/device_is_integrity_capable
Date: July 2014
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Indicates whether a storage device is capable of storing
integrity metadata. Set if the device is T10 PI-capable.
This flag is set to 1 if the storage media is formatted
with T10 Protection Information. If the storage media is
not formatted with T10 Protection Information, this flag
is set to 0.
What: /sys/block/<disk>/integrity/format
Date: June 2008
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Metadata format for integrity capable block device.
E.g. T10-DIF-TYPE1-CRC.
This field describes the type of T10 Protection Information
that the block device can send and receive.
If the device can store application integrity metadata but
no T10 Protection Information profile is used, this field
contains "nop".
If the device does not support integrity metadata, this
field contains "none".
What: /sys/block/<disk>/integrity/protection_interval_bytes
Date: July 2015
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Describes the number of data bytes which are protected
by one integrity tuple. Typically the device's logical
block size.
What: /sys/block/<disk>/integrity/read_verify
Date: June 2008
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Indicates whether the block layer should verify the
integrity of read requests serviced by devices that
support sending integrity metadata.
What: /sys/block/<disk>/integrity/tag_size
Date: June 2008
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Number of bytes of integrity tag space available per
protection_interval_bytes, which is typically
the device's logical block size.
This field describes the size of the application tag
if the storage device is formatted with T10 Protection
Information and permits use of the application tag.
The tag_size is reported in bytes and indicates the
space available for adding an opaque tag to each block
(protection_interval_bytes).
If the device does not support T10 Protection Information
(even if the device provides application integrity
metadata space), this field is set to 0.
What: /sys/block/<disk>/integrity/write_generate
Date: June 2008
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Indicates whether the block layer should automatically
generate checksums for write requests bound for
devices that support receiving integrity metadata.
What: /sys/block/<disk>/partscan
Date: May 2024
Contact: Christoph Hellwig <hch@lst.de>
Description:
The /sys/block/<disk>/partscan files reports if partition
scanning is enabled for the disk. It returns "1" if partition
scanning is enabled, or "0" if not. The value type is a 32-bit
unsigned integer, but only "0" and "1" are valid values.
What: /sys/block/<disk>/<partition>/alignment_offset
Date: April 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Storage devices may report a physical block size that is
bigger than the logical block size (for instance a drive
with 4KB physical sectors exposing 512-byte logical
blocks to the operating system). This parameter
indicates how many bytes the beginning of the partition
is offset from the disk's natural alignment.
What: /sys/block/<disk>/<partition>/discard_alignment
Date: May 2011
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
Devices that support discard functionality may
internally allocate space in units that are bigger than
the exported logical block size. The discard_alignment
parameter indicates how many bytes the beginning of the
partition is offset from the internal allocation unit's
natural alignment.
What: /sys/block/<disk>/<partition>/stat
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
Description:
The /sys/block/<disk>/<partition>/stat files display the
I/O statistics of partition <partition>. The format is the
same as the format of /sys/block/<disk>/stat.
What: /sys/block/<disk>/queue/add_random
Date: June 2010
Contact: linux-block@vger.kernel.org
Description:
[RW] This file allows to turn off the disk entropy contribution.
Default value of this file is '1'(on).
What: /sys/block/<disk>/queue/chunk_sectors
Date: September 2016
Contact: Hannes Reinecke <hare@suse.com>
Description:
[RO] chunk_sectors has different meaning depending on the type
of the disk. For a RAID device (dm-raid), chunk_sectors
indicates the size in 512B sectors of the RAID volume stripe
segment. For a zoned block device, either host-aware or
host-managed, chunk_sectors indicates the size in 512B sectors
of the zones of the device, with the eventual exception of the
last zone of the device which may be smaller.
What: /sys/block/<disk>/queue/crypto/
Date: February 2022
Contact: linux-block@vger.kernel.org
Description:
The presence of this subdirectory of /sys/block/<disk>/queue/
indicates that the device supports inline encryption. This
subdirectory contains files which describe the inline encryption
capabilities of the device. For more information about inline
encryption, refer to Documentation/block/inline-encryption.rst.
What: /sys/block/<disk>/queue/crypto/hw_wrapped_keys
Date: February 2025
Contact: linux-block@vger.kernel.org
Description:
[RO] The presence of this file indicates that the device
supports hardware-wrapped inline encryption keys, i.e. key blobs
that can only be unwrapped and used by dedicated hardware. For
more information about hardware-wrapped inline encryption keys,
see Documentation/block/inline-encryption.rst.
What: /sys/block/<disk>/queue/crypto/max_dun_bits
Date: February 2022
Contact: linux-block@vger.kernel.org
Description:
[RO] This file shows the maximum length, in bits, of data unit
numbers accepted by the device in inline encryption requests.
What: /sys/block/<disk>/queue/crypto/modes/<mode>
Date: February 2022
Contact: linux-block@vger.kernel.org
Description:
[RO] For each crypto mode (i.e., encryption/decryption
algorithm) the device supports with inline encryption, a file
will exist at this location. It will contain a hexadecimal
number that is a bitmask of the supported data unit sizes, in
bytes, for that crypto mode.
Currently, the crypto modes that may be supported are:
* AES-256-XTS
* AES-128-CBC-ESSIV
* Adiantum
For example, if a device supports AES-256-XTS inline encryption
with data unit sizes of 512 and 4096 bytes, the file
/sys/block/<disk>/queue/crypto/modes/AES-256-XTS will exist and
will contain "0x1200".
What: /sys/block/<disk>/queue/crypto/num_keyslots
Date: February 2022
Contact: linux-block@vger.kernel.org
Description:
[RO] This file shows the number of keyslots the device has for
use with inline encryption.
What: /sys/block/<disk>/queue/crypto/raw_keys
Date: February 2025
Contact: linux-block@vger.kernel.org
Description:
[RO] The presence of this file indicates that the device
supports raw inline encryption keys, i.e. keys that are managed
in raw, plaintext form in software.
What: /sys/block/<disk>/queue/dax
Date: June 2016
Contact: linux-block@vger.kernel.org
Description:
[RO] This file indicates whether the device supports Direct
Access (DAX), used by CPU-addressable storage to bypass the
pagecache. It shows '1' if true, '0' if not.
What: /sys/block/<disk>/queue/discard_granularity
Date: May 2011
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] Devices that support discard functionality may internally
allocate space using units that are bigger than the logical
block size. The discard_granularity parameter indicates the size
of the internal allocation unit in bytes if reported by the
device. Otherwise the discard_granularity will be set to match
the device's physical block size. A discard_granularity of 0
means that the device does not support discard functionality.
What: /sys/block/<disk>/queue/discard_max_bytes
Date: May 2011
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RW] While discard_max_hw_bytes is the hardware limit for the
device, this setting is the software limit. Some devices exhibit
large latencies when large discards are issued, setting this
value lower will make Linux issue smaller discards and
potentially help reduce latencies induced by large discard
operations.
What: /sys/block/<disk>/queue/discard_max_hw_bytes
Date: July 2015
Contact: linux-block@vger.kernel.org
Description:
[RO] Devices that support discard functionality may have
internal limits on the number of bytes that can be trimmed or
unmapped in a single operation. The `discard_max_hw_bytes`
parameter is set by the device driver to the maximum number of
bytes that can be discarded in a single operation. Discard
requests issued to the device must not exceed this limit. A
`discard_max_hw_bytes` value of 0 means that the device does not
support discard functionality.
What: /sys/block/<disk>/queue/discard_zeroes_data
Date: May 2011
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] Will always return 0. Don't rely on any specific behavior
for discards, and don't read this file.
What: /sys/block/<disk>/queue/dma_alignment
Date: May 2022
Contact: linux-block@vger.kernel.org
Description:
Reports the alignment that user space addresses must have to be
used for raw block device access with O_DIRECT and other driver
specific passthrough mechanisms.
What: /sys/block/<disk>/queue/fua
Date: May 2018
Contact: linux-block@vger.kernel.org
Description:
[RO] Whether or not the block driver supports the FUA flag for
write requests. FUA stands for Force Unit Access. If the FUA
flag is set that means that write requests must bypass the
volatile cache of the storage device.
What: /sys/block/<disk>/queue/hw_sector_size
Date: January 2008
Contact: linux-block@vger.kernel.org
Description:
[RO] This is the hardware sector size of the device, in bytes.
What: /sys/block/<disk>/queue/independent_access_ranges/
Date: October 2021
Contact: linux-block@vger.kernel.org
Description:
[RO] The presence of this sub-directory of the
/sys/block/xxx/queue/ directory indicates that the device is
capable of executing requests targeting different sector ranges
in parallel. For instance, single LUN multi-actuator hard-disks
will have an independent_access_ranges directory if the device
correctly advertises the sector ranges of its actuators.
The independent_access_ranges directory contains one directory
per access range, with each range described using the sector
(RO) attribute file to indicate the first sector of the range
and the nr_sectors (RO) attribute file to indicate the total
number of sectors in the range starting from the first sector of
the range. For example, a dual-actuator hard-disk will have the
following independent_access_ranges entries.::
$ tree /sys/block/<disk>/queue/independent_access_ranges/
/sys/block/<disk>/queue/independent_access_ranges/
|-- 0
| |-- nr_sectors
| `-- sector
`-- 1
|-- nr_sectors
`-- sector
The sector and nr_sectors attributes use 512B sector unit,
regardless of the actual block size of the device. Independent
access ranges do not overlap and include all sectors within the
device capacity. The access ranges are numbered in increasing
order of the range start sector, that is, the sector attribute
of range 0 always has the value 0.
What: /sys/block/<disk>/queue/io_poll
Date: November 2015
Contact: linux-block@vger.kernel.org
Description:
[RW] When read, this file shows whether polling is enabled (1)
or disabled (0). Writing '0' to this file will disable polling
for this device. Writing any non-zero value will enable this
feature.
What: /sys/block/<disk>/queue/io_poll_delay
Date: November 2016
Contact: linux-block@vger.kernel.org
Description:
[RW] This was used to control what kind of polling will be
performed. It is now fixed to -1, which is classic polling.
In this mode, the CPU will repeatedly ask for completions
without giving up any time.
<deprecated>
What: /sys/block/<disk>/queue/io_timeout
Date: November 2018
Contact: Weiping Zhang <zhangweiping@didiglobal.com>
Description:
[RW] io_timeout is the request timeout in milliseconds. If a
request does not complete in this time then the block driver
timeout handler is invoked. That timeout handler can decide to
retry the request, to fail it or to start a device recovery
strategy.
What: /sys/block/<disk>/queue/iostats
Date: January 2009
Contact: linux-block@vger.kernel.org
Description:
[RW] This file is used to control (on/off) the iostats
accounting of the disk.
What: /sys/block/<disk>/queue/iostats_passthrough
Date: October 2024
Contact: linux-block@vger.kernel.org
Description:
[RW] This file is used to control (on/off) the iostats
accounting of the disk for passthrough commands.
What: /sys/block/<disk>/queue/logical_block_size
Date: May 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] This is the smallest unit the storage device can address.
It is typically 512 bytes.
What: /sys/block/<disk>/queue/max_active_zones
Date: July 2020
Contact: Niklas Cassel <niklas.cassel@wdc.com>
Description:
[RO] For zoned block devices (zoned attribute indicating
"host-managed" or "host-aware"), the sum of zones belonging to
any of the zone states: EXPLICIT OPEN, IMPLICIT OPEN or CLOSED,
is limited by this value. If this value is 0, there is no limit.
If the host attempts to exceed this limit, the driver should
report this error with BLK_STS_ZONE_ACTIVE_RESOURCE, which user
space may see as the EOVERFLOW errno.
What: /sys/block/<disk>/queue/max_discard_segments
Date: February 2017
Contact: linux-block@vger.kernel.org
Description:
[RO] The maximum number of DMA scatter/gather entries in a
discard request.
What: /sys/block/<disk>/queue/max_hw_sectors_kb
Date: September 2004
Contact: linux-block@vger.kernel.org
Description:
[RO] This is the maximum number of kilobytes supported in a
single data transfer.
What: /sys/block/<disk>/queue/max_integrity_segments
Date: September 2010
Contact: linux-block@vger.kernel.org
Description:
[RO] Maximum number of elements in a DMA scatter/gather list
with integrity data that will be submitted by the block layer
core to the associated block driver.
What: /sys/block/<disk>/queue/max_open_zones
Date: July 2020
Contact: Niklas Cassel <niklas.cassel@wdc.com>
Description:
[RO] For zoned block devices (zoned attribute indicating
"host-managed" or "host-aware"), the sum of zones belonging to
any of the zone states: EXPLICIT OPEN or IMPLICIT OPEN, is
limited by this value. If this value is 0, there is no limit.
What: /sys/block/<disk>/queue/max_sectors_kb
Date: September 2004
Contact: linux-block@vger.kernel.org
Description:
[RW] This is the maximum number of kilobytes that the block
layer will allow for a filesystem request. Must be smaller than
or equal to the maximum size allowed by the hardware. Write 0
to use default kernel settings.
What: /sys/block/<disk>/queue/max_segment_size
Date: March 2010
Contact: linux-block@vger.kernel.org
Description:
[RO] Maximum size in bytes of a single element in a DMA
scatter/gather list.
What: /sys/block/<disk>/queue/max_write_streams
Date: November 2024
Contact: linux-block@vger.kernel.org
Description:
[RO] Maximum number of write streams supported, 0 if not
supported. If supported, valid values are 1 through
max_write_streams, inclusive.
What: /sys/block/<disk>/queue/write_stream_granularity
Date: November 2024
Contact: linux-block@vger.kernel.org
Description:
[RO] Granularity of a write stream in bytes. The granularity
of a write stream is the size that should be discarded or
overwritten together to avoid write amplification in the device.
What: /sys/block/<disk>/queue/max_segments
Date: March 2010
Contact: linux-block@vger.kernel.org
Description:
[RO] Maximum number of elements in a DMA scatter/gather list
that is submitted to the associated block driver.
What: /sys/block/<disk>/queue/minimum_io_size
Date: April 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] Storage devices may report a granularity or preferred
minimum I/O size which is the smallest request the device can
perform without incurring a performance penalty. For disk
drives this is often the physical block size. For RAID arrays
it is often the stripe chunk size. A properly aligned multiple
of minimum_io_size is the preferred request size for workloads
where a high number of I/O operations is desired.
What: /sys/block/<disk>/queue/nomerges
Date: January 2010
Contact: linux-block@vger.kernel.org
Description:
[RW] Standard I/O elevator operations include attempts to merge
contiguous I/Os. For known random I/O loads these attempts will
always fail and result in extra cycles being spent in the
kernel. This allows one to turn off this behavior on one of two
ways: When set to 1, complex merge checks are disabled, but the
simple one-shot merges with the previous I/O request are
enabled. When set to 2, all merge tries are disabled. The
default value is 0 - which enables all types of merge tries.
What: /sys/block/<disk>/queue/nr_requests
Date: July 2003
Contact: linux-block@vger.kernel.org
Description:
[RW] This controls how many requests may be allocated in the
block layer for read or write requests. Note that the total
allocated number may be twice this amount, since it applies only
to reads or writes (not the accumulated sum).
To avoid priority inversion through request starvation, a
request queue maintains a separate request pool per each cgroup
when CONFIG_BLK_CGROUP is enabled, and this parameter applies to
each such per-block-cgroup request pool. IOW, if there are N
block cgroups, each request queue may have up to N request
pools, each independently regulated by nr_requests.
What: /sys/block/<disk>/queue/nr_zones
Date: November 2018
Contact: Damien Le Moal <damien.lemoal@wdc.com>
Description:
[RO] nr_zones indicates the total number of zones of a zoned
block device ("host-aware" or "host-managed" zone model). For
regular block devices, the value is always 0.
What: /sys/block/<disk>/queue/optimal_io_size
Date: April 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] Storage devices may report an optimal I/O size, which is
the device's preferred unit for sustained I/O. This is rarely
reported for disk drives. For RAID arrays it is usually the
stripe width or the internal track size. A properly aligned
multiple of optimal_io_size is the preferred request size for
workloads where sustained throughput is desired. If no optimal
I/O size is reported this file contains 0.
What: /sys/block/<disk>/queue/physical_block_size
Date: May 2009
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] This is the smallest unit a physical storage device can
write atomically. It is usually the same as the logical block
size but may be bigger. One example is SATA drives with 4KB
sectors that expose a 512-byte logical block size to the
operating system. For stacked block devices the
physical_block_size variable contains the maximum
physical_block_size of the component devices.
What: /sys/block/<disk>/queue/read_ahead_kb
Date: May 2004
Contact: linux-block@vger.kernel.org
Description:
[RW] Maximum number of kilobytes to read-ahead for filesystems
on this block device.
For MADV_HUGEPAGE, the readahead size may exceed this setting
since its granularity is based on the hugepage size.
What: /sys/block/<disk>/queue/rotational
Date: January 2009
Contact: linux-block@vger.kernel.org
Description:
[RW] This file is used to stat if the device is of rotational
type or non-rotational type.
What: /sys/block/<disk>/queue/rq_affinity
Date: September 2008
Contact: linux-block@vger.kernel.org
Description:
[RW] If this option is '1', the block layer will migrate request
completions to the cpu "group" that originally submitted the
request. For some workloads this provides a significant
reduction in CPU cycles due to caching effects.
For storage configurations that need to maximize distribution of
completion processing setting this option to '2' forces the
completion to run on the requesting cpu (bypassing the "group"
aggregation logic).
What: /sys/block/<disk>/queue/scheduler
Date: October 2004
Contact: linux-block@vger.kernel.org
Description:
[RW] When read, this file will display the current and available
IO schedulers for this block device. The currently active IO
scheduler will be enclosed in [] brackets. Writing an IO
scheduler name to this file will switch control of this block
device to that new IO scheduler. Note that writing an IO
scheduler name to this file will attempt to load that IO
scheduler module, if it isn't already present in the system.
What: /sys/block/<disk>/queue/stable_writes
Date: September 2020
Contact: linux-block@vger.kernel.org
Description:
[RW] This file will contain '1' if memory must not be modified
while it is being used in a write request to this device. When
this is the case and the kernel is performing writeback of a
page, the kernel will wait for writeback to complete before
allowing the page to be modified again, rather than allowing
immediate modification as is normally the case. This
restriction arises when the device accesses the memory multiple
times where the same data must be seen every time -- for
example, once to calculate a checksum and once to actually write
the data. If no such restriction exists, this file will contain
'0'. This file is writable for testing purposes.
What: /sys/block/<disk>/queue/virt_boundary_mask
Date: April 2021
Contact: linux-block@vger.kernel.org
Description:
[RO] This file shows the I/O segment memory alignment mask for
the block device. I/O requests to this device will be split
between segments wherever either the memory address of the end
of the previous segment or the memory address of the beginning
of the current segment is not aligned to virt_boundary_mask + 1
bytes.
What: /sys/block/<disk>/queue/wbt_lat_usec
Date: November 2016
Contact: linux-block@vger.kernel.org
Description:
[RW] If the device is registered for writeback throttling, then
this file shows the target minimum read latency. If this latency
is exceeded in a given window of time (see wb_window_usec), then
the writeback throttling will start scaling back writes. Writing
a value of '0' to this file disables the feature. Writing a
value of '-1' to this file resets the value to the default
setting.
What: /sys/block/<disk>/queue/write_cache
Date: April 2016
Contact: linux-block@vger.kernel.org
Description:
[RW] When read, this file will display whether the device has
write back caching enabled or not. It will return "write back"
for the former case, and "write through" for the latter. Writing
to this file can change the kernels view of the device, but it
doesn't alter the device state. This means that it might not be
safe to toggle the setting from "write back" to "write through",
since that will also eliminate cache flushes issued by the
kernel.
What: /sys/block/<disk>/queue/write_same_max_bytes
Date: January 2012
Contact: Martin K. Petersen <martin.petersen@oracle.com>
Description:
[RO] Some devices support a write same operation in which a
single data block can be written to a range of several
contiguous blocks on storage. This can be used to wipe areas on
disk or to initialize drives in a RAID configuration.
write_same_max_bytes indicates how many bytes can be written in
a single write same command. If write_same_max_bytes is 0, write
same is not supported by the device.
What: /sys/block/<disk>/queue/write_zeroes_max_bytes
Date: November 2016
Contact: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Description:
[RO] Devices that support write zeroes operation in which a
single request can be issued to zero out the range of contiguous
blocks on storage without having any payload in the request.
This can be used to optimize writing zeroes to the devices.
write_zeroes_max_bytes indicates how many bytes can be written
in a single write zeroes command. If write_zeroes_max_bytes is
0, write zeroes is not supported by the device.
What: /sys/block/<disk>/queue/write_zeroes_unmap_max_hw_bytes
Date: January 2025
Contact: Zhang Yi <yi.zhang@huawei.com>
Description:
[RO] This file indicates whether a device supports zeroing data
in a specified block range without incurring the cost of
physically writing zeroes to the media for each individual
block. If this parameter is set to write_zeroes_max_bytes, the
device implements a zeroing operation which opportunistically
avoids writing zeroes to media while still guaranteeing that
subsequent reads from the specified block range will return
zeroed data. This operation is a best-effort optimization, a
device may fall back to physically writing zeroes to the media
due to other factors such as misalignment or being asked to
clear a block range smaller than the device's internal
allocation unit. If this parameter is set to 0, the device may
have to write each logical block media during a zeroing
operation.
What: /sys/block/<disk>/queue/write_zeroes_unmap_max_bytes
Date: January 2025
Contact: Zhang Yi <yi.zhang@huawei.com>
Description:
[RW] While write_zeroes_unmap_max_hw_bytes is the hardware limit
for the device, this setting is the software limit. Since the
unmap write zeroes operation is a best-effort optimization, some
devices may still physically writing zeroes to media. So the
speed of this operation is not guaranteed. Writing a value of
'0' to this file disables this operation. Otherwise, this
parameter should be equal to write_zeroes_unmap_max_hw_bytes.
What: /sys/block/<disk>/queue/zone_append_max_bytes
Date: May 2020
Contact: linux-block@vger.kernel.org
Description:
[RO] This is the maximum number of bytes that can be written to
a sequential zone of a zoned block device using a zone append
write operation (REQ_OP_ZONE_APPEND). This value is always 0 for
regular block devices.
What: /sys/block/<disk>/queue/zone_write_granularity
Date: January 2021
Contact: linux-block@vger.kernel.org
Description:
[RO] This indicates the alignment constraint, in bytes, for
write operations in sequential zones of zoned block devices
(devices with a zoned attributed that reports "host-managed" or
"host-aware"). This value is always 0 for regular block devices.
What: /sys/block/<disk>/queue/zoned
Date: September 2016
Contact: Damien Le Moal <damien.lemoal@wdc.com>
Description:
[RO] zoned indicates if the device is a zoned block device and
the zone model of the device if it is indeed zoned. The
possible values indicated by zoned are "none" for regular block
devices and "host-aware" or "host-managed" for zoned block
devices. The characteristics of host-aware and host-managed
zoned block devices are described in the ZBC (Zoned Block
Commands) and ZAC (Zoned Device ATA Command Set) standards.
These standards also define the "drive-managed" zone model.
However, since drive-managed zoned block devices do not support
zone commands, they will be treated as regular block devices and
zoned will report "none".
What: /sys/block/<disk>/hidden
Date: March 2023
Contact: linux-block@vger.kernel.org
Description:
[RO] the block device is hidden. it doesn’t produce events, and
can’t be opened from userspace or using blkdev_get*.
Used for the underlying components of multipath devices.
What: /sys/block/<disk>/stat
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
Description:
The /sys/block/<disk>/stat files displays the I/O
statistics of disk <disk>. They contain 11 fields:
== ==============================================
1 reads completed successfully
2 reads merged
3 sectors read
4 time spent reading (ms)
5 writes completed
6 writes merged
7 sectors written
8 time spent writing (ms)
9 I/Os currently in progress
10 time spent doing I/Os (ms)
11 weighted time spent doing I/Os (ms)
12 discards completed
13 discards merged
14 sectors discarded
15 time spent discarding (ms)
16 flush requests completed
17 time spent flushing (ms)
== ==============================================
For more details refer Documentation/admin-guide/iostats.rst
Reference in a new issue View git blame Copy permalink