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Performance tuning
44 Dell EMC SC Series: Red Hat Enterprise Linux Best Practices | CML1031
Show the current I/O schedule:
• Show all sd devices:
# egrep "*" /sys/block/sd*/queue/scheduler
/sys/block/sda/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdb/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdc/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdd/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sde/queue/scheduler:noop anticipatory deadline [cfq]
• Show all dm-multipath devices and the associated sd devices:
# multipath -ll | sed -rn 's/.*(dm-[[:digit:]]+|sd[[:alpha:]]+).*/\1/p'
|xargs -I % echo egrep -H \"*\" /sys/block/%/queue/scheduler | bash
/sys/block/dm-2/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdb/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdd/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdc/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sde/queue/scheduler:noop anticipatory deadline [cfq]
Dynamically change the I/O schedule by writing to the device’s scheduler sysfs file:
The change does not persist after system reboots.
• Change a single sd device:
# echo deadline > /sys/block/sda/queue/scheduler
• Change all sd devices:
# ls -1 /sys/block/sd[a-z]/queue/scheduler |xargs -I % echo echo deadline
">" %|bash
• Change a single dm-multipath device and the associated sd devices:
# multipath -ll $MPATH_NAME | sed -rn 's/.*(dm-
[[:digit:]]+|sd[[:alpha:]]+).*/\1/p' | xargs -I % echo echo deadline ">"
/sys/block/%/queue/scheduler | bash
• Change all dm-multipath devices and the associated sd devices:
This command is the same as the single dm-multipath option above except the $MPATH_NAME
argument is removed.