Re: use ZFS for OSDs

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On Wed, 29 Oct 2014 15:32:57 +0000 Michal Kozanecki wrote:

[snip]
> With Ceph handling the
> redundancy at the OSD level I saw no need for using ZFS mirroring or
> zraid, instead if ZFS detects corruption instead of self-healing it
> sends a read failure of the pg file to ceph, and then ceph's scrub
> mechanisms should then repair/replace the pg file using a good replica
> elsewhere on the cluster. ZFS + ceph are a beautiful bitrot fighting
> match!
> 
Could you elaborate on that? 
AFAIK Ceph currently has no way to determine which of the replicas is
"good", one such failed PG object will require you to do a manual repair
after the scrub and hope that two surviving replicas (assuming a size of
3) are identical. If not, start tossing a coin.
Ideally Ceph would have a way to know what happened (as in, it's a
checksum and not a real I/O error) and do a rebuild of that object itself.

On an other note, have you done any tests using the ZFS compression?
I'm wondering what the performance impact and efficiency are.

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi@xxxxxxx   	Global OnLine Japan/Fusion Communications
http://www.gol.com/
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