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4363ac7c13
The WRITE SAME command supported on some SCSI devices allows the same block to be efficiently replicated throughout a block range. Only a single logical block is transferred from the host and the storage device writes the same data to all blocks described by the I/O. This patch implements support for WRITE SAME in the block layer. The blkdev_issue_write_same() function can be used by filesystems and block drivers to replicate a buffer across a block range. This can be used to efficiently initialize software RAID devices, etc. Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> Acked-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
223 lines
8.4 KiB
Plaintext
223 lines
8.4 KiB
Plaintext
What: /sys/block/<disk>/stat
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Date: February 2008
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Contact: Jerome Marchand <jmarchan@redhat.com>
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Description:
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The /sys/block/<disk>/stat files displays the I/O
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statistics of disk <disk>. They contain 11 fields:
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1 - reads completed successfully
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2 - reads merged
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3 - sectors read
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4 - time spent reading (ms)
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5 - writes completed
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6 - writes merged
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7 - sectors written
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8 - time spent writing (ms)
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9 - I/Os currently in progress
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10 - time spent doing I/Os (ms)
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11 - weighted time spent doing I/Os (ms)
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For more details refer Documentation/iostats.txt
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What: /sys/block/<disk>/<part>/stat
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Date: February 2008
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Contact: Jerome Marchand <jmarchan@redhat.com>
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Description:
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The /sys/block/<disk>/<part>/stat files display the
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I/O statistics of partition <part>. The format is the
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same as the above-written /sys/block/<disk>/stat
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format.
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What: /sys/block/<disk>/integrity/format
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Date: June 2008
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Metadata format for integrity capable block device.
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E.g. T10-DIF-TYPE1-CRC.
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What: /sys/block/<disk>/integrity/read_verify
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Date: June 2008
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Indicates whether the block layer should verify the
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integrity of read requests serviced by devices that
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support sending integrity metadata.
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What: /sys/block/<disk>/integrity/tag_size
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Date: June 2008
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Number of bytes of integrity tag space available per
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512 bytes of data.
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What: /sys/block/<disk>/integrity/write_generate
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Date: June 2008
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Indicates whether the block layer should automatically
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generate checksums for write requests bound for
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devices that support receiving integrity metadata.
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What: /sys/block/<disk>/alignment_offset
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Date: April 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Storage devices may report a physical block size that is
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bigger than the logical block size (for instance a drive
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with 4KB physical sectors exposing 512-byte logical
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blocks to the operating system). This parameter
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indicates how many bytes the beginning of the device is
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offset from the disk's natural alignment.
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What: /sys/block/<disk>/<partition>/alignment_offset
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Date: April 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Storage devices may report a physical block size that is
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bigger than the logical block size (for instance a drive
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with 4KB physical sectors exposing 512-byte logical
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blocks to the operating system). This parameter
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indicates how many bytes the beginning of the partition
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is offset from the disk's natural alignment.
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What: /sys/block/<disk>/queue/logical_block_size
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Date: May 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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This is the smallest unit the storage device can
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address. It is typically 512 bytes.
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What: /sys/block/<disk>/queue/physical_block_size
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Date: May 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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This is the smallest unit a physical storage device can
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write atomically. It is usually the same as the logical
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block size but may be bigger. One example is SATA
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drives with 4KB sectors that expose a 512-byte logical
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block size to the operating system. For stacked block
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devices the physical_block_size variable contains the
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maximum physical_block_size of the component devices.
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What: /sys/block/<disk>/queue/minimum_io_size
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Date: April 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Storage devices may report a granularity or preferred
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minimum I/O size which is the smallest request the
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device can perform without incurring a performance
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penalty. For disk drives this is often the physical
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block size. For RAID arrays it is often the stripe
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chunk size. A properly aligned multiple of
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minimum_io_size is the preferred request size for
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workloads where a high number of I/O operations is
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desired.
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What: /sys/block/<disk>/queue/optimal_io_size
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Date: April 2009
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Storage devices may report an optimal I/O size, which is
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the device's preferred unit for sustained I/O. This is
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rarely reported for disk drives. For RAID arrays it is
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usually the stripe width or the internal track size. A
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properly aligned multiple of optimal_io_size is the
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preferred request size for workloads where sustained
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throughput is desired. If no optimal I/O size is
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reported this file contains 0.
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What: /sys/block/<disk>/queue/nomerges
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Date: January 2010
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Contact:
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Description:
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Standard I/O elevator operations include attempts to
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merge contiguous I/Os. For known random I/O loads these
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attempts will always fail and result in extra cycles
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being spent in the kernel. This allows one to turn off
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this behavior on one of two ways: When set to 1, complex
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merge checks are disabled, but the simple one-shot merges
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with the previous I/O request are enabled. When set to 2,
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all merge tries are disabled. The default value is 0 -
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which enables all types of merge tries.
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What: /sys/block/<disk>/discard_alignment
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Date: May 2011
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Devices that support discard functionality may
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internally allocate space in units that are bigger than
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the exported logical block size. The discard_alignment
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parameter indicates how many bytes the beginning of the
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device is offset from the internal allocation unit's
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natural alignment.
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What: /sys/block/<disk>/<partition>/discard_alignment
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Date: May 2011
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Devices that support discard functionality may
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internally allocate space in units that are bigger than
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the exported logical block size. The discard_alignment
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parameter indicates how many bytes the beginning of the
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partition is offset from the internal allocation unit's
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natural alignment.
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What: /sys/block/<disk>/queue/discard_granularity
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Date: May 2011
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Devices that support discard functionality may
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internally allocate space using units that are bigger
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than the logical block size. The discard_granularity
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parameter indicates the size of the internal allocation
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unit in bytes if reported by the device. Otherwise the
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discard_granularity will be set to match the device's
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physical block size. A discard_granularity of 0 means
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that the device does not support discard functionality.
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What: /sys/block/<disk>/queue/discard_max_bytes
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Date: May 2011
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Devices that support discard functionality may have
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internal limits on the number of bytes that can be
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trimmed or unmapped in a single operation. Some storage
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protocols also have inherent limits on the number of
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blocks that can be described in a single command. The
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discard_max_bytes parameter is set by the device driver
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to the maximum number of bytes that can be discarded in
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a single operation. Discard requests issued to the
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device must not exceed this limit. A discard_max_bytes
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value of 0 means that the device does not support
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discard functionality.
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What: /sys/block/<disk>/queue/discard_zeroes_data
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Date: May 2011
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Devices that support discard functionality may return
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stale or random data when a previously discarded block
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is read back. This can cause problems if the filesystem
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expects discarded blocks to be explicitly cleared. If a
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device reports that it deterministically returns zeroes
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when a discarded area is read the discard_zeroes_data
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parameter will be set to one. Otherwise it will be 0 and
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the result of reading a discarded area is undefined.
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What: /sys/block/<disk>/queue/write_same_max_bytes
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Date: January 2012
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Contact: Martin K. Petersen <martin.petersen@oracle.com>
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Description:
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Some devices support a write same operation in which a
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single data block can be written to a range of several
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contiguous blocks on storage. This can be used to wipe
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areas on disk or to initialize drives in a RAID
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configuration. write_same_max_bytes indicates how many
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bytes can be written in a single write same command. If
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write_same_max_bytes is 0, write same is not supported
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by the device.
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