Hi list,
During my write test,I find there are always some of the osds have high
fs_apply_latency（1k-5kms,2-8times more than others）. At first I think it is
caused by unbalanced pg distribution, but after I reweight the osds the problem
hasn't gone away.
I looked into the osds with high latency and find one thing in common.There are
alot of read activities on these osds.Result of iostat shows there are 400-500
r/s and 2000-3000 rKB/s on these high latnecy osds while the normal osds have
around 100 r/s 300-400 rKB/s.
I tried to restart osd daemon with high latency.It did became normal sometime
but there will be another high latency osds come out.And the new high latency
osd has the same high read activities.
What are these read activities for? Is there a way to lower the latency?
Thanks
2018-03-10
shadowlin
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