[PVE-User] Some operations wildly slow with ceph rbd

Adam Thompson athompso at athompso.net
Mon Jan 5 16:11:24 CET 2015


I see problems with making backups but not with restoring them.  I just used the backup and restore features to move about a dozen VMs into a new RBD-based cluster and it went very smoothly and quickly.
I have noticed previously that taking backups of an rbd-based VM takes forever and sometimes deadlocked the cluster service by consuming all available memory.
But I haven't experienced either of your specific issues.
-Adam

On January 5, 2015 8:52:50 AM CST, Lindsay Mathieson <lindsay.mathieson at gmail.com> wrote:
>I have my ceph cluster setup - 6 osd's on 2 ndoes with ssd journals.
>Its fast 
>enough for my requirements - 140 MBS/s seq write, 500 MB/s seq read,
>IOPS are 
>reasonable to.
>
>I have 20 VM's running ver rbd, they perform quite well. responsive
>desktops 
>and servers, no complaints there.
>
>Where it all goes wrong is snapshots and backup restores.
>
>Snapshots I've mentioned before, over 10 minutes to take a snapshot of
>a small 
>VM is wrong. The actual disk snapshot is near instant, its the live
>state that 
>takes all the time. The same VM only takes 30 seconds to snapshot on
>cephfs or 
>NFS. The one rollback I tried to 40 min and was corrupted at the end.
>
>Restores - I started a VM restore this evening, this is one I've done
>before 
>on our crappy NAS nfs server - takes about 30  min.
>
>2.5 *hours* later it reached 20% at that rate it would be 8 hours to
>finish.
>
>I cancelled it and restarted the restore to cephfs (same storage). It
>takes it 
>8 *minutes* to get to 20%
>
>Oddly, a disk migration from cephfs to rbd is much faster - about 40min
>for 
>the same virtual disk. Its literally much quicker to restore VM's to
>cephfs, 
>then migrate the disk to ceph rbd.
>
>
>
>
>Any idea why snapshot and backup restore operations are so slow on rbd?
>it is 
>literally making the snapshot and backup function useless for my
>purposes. 
>Surely I'm not the only one for whom this is a problem.
>-- 
>Lindsay
>
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