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Enhanced partition statistics: documentation update
Update the documentation to reflect the change in userspace interface.
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
authored by Jerome Marchand and committed by Jens Axboe 0e53c2be c3c930d9
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Documentation/ABI/testing/procfs-diskstats
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Documentation/ABI/testing/procfs-diskstats
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What: /proc/diskstats
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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 /proc/diskstats file displays the I/O statistics
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of block devices. Each line contains the following 14
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fields:
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1 - major number
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2 - minor mumber
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3 - device name
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4 - reads completed succesfully
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5 - reads merged
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6 - sectors read
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7 - time spent reading (ms)
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8 - writes completed
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9 - writes merged
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10 - sectors written
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11 - time spent writing (ms)
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12 - I/Os currently in progress
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13 - time spent doing I/Os (ms)
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14 - weighted time spent doing I/Os (ms)
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For more details refer to Documentation/iostats.txt
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Documentation/ABI/testing/sysfs-block
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Documentation/ABI/testing/sysfs-block
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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 succesfully
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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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Documentation/iostats.txt
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Documentation/iostats.txt
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Each set of stats only applies to the indicated device; if you want
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system-wide stats you'll have to find all the devices and sum them all up.
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Field 1 -- # of reads issued
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This is the total number of reads completed successfully.
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Field 2 -- # of reads merged, field 6 -- # of writes merged
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Reads and writes which are adjacent to each other may be merged for
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words, the number of reads for partitions is counted slightly before time
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of queuing for partitions, and at completion for whole disks. This is
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a subtle distinction that is probably uninteresting for most cases.
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Additional notes
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Each set of stats only applies to the indicated device; if you want
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system-wide stats you'll have to find all the devices and sum them all up.
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Field 1 -- # of reads completed
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This is the total number of reads completed successfully.
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Field 2 -- # of reads merged, field 6 -- # of writes merged
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Reads and writes which are adjacent to each other may be merged for
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words, the number of reads for partitions is counted slightly before time
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of queuing for partitions, and at completion for whole disks. This is
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a subtle distinction that is probably uninteresting for most cases.
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More significant is the error induced by counting the numbers of
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reads/writes before merges for partitions and after for disks. Since a
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typical workload usually contains a lot of successive and adjacent requests,
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the number of reads/writes issued can be several times higher than the
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number of reads/writes completed.
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In 2.6.25, the full statistic set is again available for partitions and
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disk and partition statistics are consistent again. Since we still don't
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keep record of the partition-relative address, an operation is attributed to
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the partition which contains the first sector of the request after the
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eventual merges. As requests can be merged across partition, this could lead
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to some (probably insignificant) innacuracy.
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Additional notes
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----------------