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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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