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This patch adds a dynamic load balancer, dm-queue-length, which balances the number of in-flight I/Os across the paths. The code is based on the patch posted by Stefan Bader: https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html Signed-off-by: Stefan Bader <stefan.bader@canonical.com> Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
40 lines
1.2 KiB
Plaintext
40 lines
1.2 KiB
Plaintext
dm-queue-length
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===============
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dm-queue-length is a path selector module for device-mapper targets,
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which selects a path with the least number of in-flight I/Os.
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The path selector name is 'queue-length'.
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Table parameters for each path: [<repeat_count>]
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<repeat_count>: The number of I/Os to dispatch using the selected
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path before switching to the next path.
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If not given, internal default is used. To check
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the default value, see the activated table.
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Status for each path: <status> <fail-count> <in-flight>
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<status>: 'A' if the path is active, 'F' if the path is failed.
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<fail-count>: The number of path failures.
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<in-flight>: The number of in-flight I/Os on the path.
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Algorithm
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=========
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dm-queue-length increments/decrements 'in-flight' when an I/O is
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dispatched/completed respectively.
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dm-queue-length selects a path with the minimum 'in-flight'.
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Examples
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========
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In case that 2 paths (sda and sdb) are used with repeat_count == 128.
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# echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \
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dmsetup create test
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#
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# dmsetup table
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test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128
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#
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# dmsetup status
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test: 0 10 multipath 2 0 0 0 1 1 E 0 2 1 8:0 A 0 0 8:16 A 0 0
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