[Openstack] cinder slow (nova issues?)

Robert van Leeuwen Robert.vanLeeuwen at spilgames.com
Tue Dec 23 08:38:19 UTC 2014

> using RDO IceHouse packages I've set up an infrastructure atop of
> RHEL6.6 and am seeing a very unpleasant performance for the storage.
>cinder-volume # dd if=/dev/zero of=baloon bs=1048576 count=200
>Results are just miserable. going from 1.2G/s down to 20M/s seems to be a big
>degradation. What should I look for? I have also tried running the same

2 suggestions to check:

* The dd command you run will just push to the filesystem write cache and never actually hits the disk before the command finishes. This explains the 1.2G/s. 
Use a command that actually syncs to disk to do performance tests. 
You can use oflag=dsync with dd or, even better, use a tool like fio or filebench.
I would also increase the filesize to make sure you are not just hitting a raid controller cache.

* Have a look at the storage node when you do the benchmark. 
Run atop or something similar to see if the storage is the actual bottleneck or if it is something on the client.

Robert van Leeuwen

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