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When running fio command to do sequential IO test, I found rrqm/s in iostat report always show zero, which means there is no merge. But avgrq-sz is not what I set in fio options(-bs=256k), only about 177k.

fio -directory=/data -direct=1 -iodepth=16 -rw=write -ioengine=libaio -bs=256k -size=1G -time_based=1 -runtime=600 -group_reporting -name=write
write: (g=0): rw=write, bs=(R) 256KiB-256KiB, (W) 256KiB-256KiB, (T) 256KiB-256KiB, ioengine=libaio, iodepth=16

device dm-3(which is LVM logical volume) is mount on /data path.

Here is iostat report(iostat -x 1 vdb dm-3)

enter image description here

rrqm/s should not be zero cause there are IO mergings

Zhiheng Sun
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1 Answers1

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fio -directory=/data -direct=1 -iodepth=16 -rw=write -ioengine=libaio -bs=256k -size=1G -time_based=1 -runtime=600 -group_reporting -name=write write: (g=0): rw=write, bs=(R) 256KiB-256KiB, (W) 256KiB-256KiB, (T) 256KiB-256KiB, ioengine=libaio, iodepth=16

It looks like this is a pure sequential write workload. So "rrqm" is possibly be zero if there was no other thread doing read. May need to check "wrqm/s" which is the number of write requests merged per second.

HardcoreSkier
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