My response is without any context to ceph or any SDS, purely how to check the 
IO bottleneck. You can then determine if its Ceph or any other process or disk.



>> MySQL can reach only 150 iops both read or writes showing 30% of IOwait.

Lower IOPS is not issue with itself as your block size might be higher. But 
MySQL doing higher block not sure.  You can check below iostat metrics to see 
why is the IO wait higher.



*  avgqu-sz(Avg queue length)                        -->  Higher the Q length 
more the IO wait

* avgrq-sz[The average size (in sectors)]     -->  Shows IOblock size( check 
this when using mysql). [ you need to calculate this based on your FS block 
size in KB & don’t just you the avgrq-sz # ]





--

Deepak







-----Original Message-----
From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of Matteo 
Dacrema
Sent: Tuesday, March 07, 2017 12:52 PM
To: ceph-users
Subject: [ceph-users] MySQL and ceph volumes



Hi All,



I have a galera cluster running on openstack with data on ceph volumes capped 
at 1500 iops for read and write ( 3000 total ).

I can’t understand why with fio I can reach 1500 iops without IOwait and MySQL 
can reach only 150 iops both read or writes showing 30% of IOwait.



I tried with fio 64k block size and various io depth ( 1.2.4.8.16….128) and I 
can’t reproduce the problem.



Anyone can tell me where I’m wrong?



Thank you

Regards

Matteo



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