On 05/30/2012 01:33 AM, Stefan Priebe - Profihost AG wrote:
I setup some tests today to try to replicate your findings (and also
check results against some previous ones I've done). I don't think I'm
seeing exactly the same results as you, but I definitely see xfs
performing worse in this specific test than btrfs. I've included the
results here.
Full results are available here:
http://nhm.ceph.com/results/mailinglist-tests/
But these tests shows exactly he same bad behaviour i'm seeing. Instead
of having a constant sequential write ratio you've heavily jumping
values. Are you able to test with XFS and 3.0.32? You'll then probably
see an absolutely constant write ratio.
Greets,
Stefan
The jumping around is due to the writes to the underlying OSD disk not
being able to keep up with the journal. I think it's more a symptom of
the problem rather than the problem itself. Presumably the OSD data
disk is performing slowly because of the number of seeks that are
happening (In my tests almost always between 40-60 on XFS, and growing
over time on btrfs). It's entirely possible that something changed
going from 3.0 to 3.4 that is causing the seek behavior to be worse.
I'll try the test again on a 3.0 kernel and record seekwatcher results
to see if the write patterns look any different.
Btw, I apologize if you mentioned this already, but are you running MONs
on the OSD nodes? Also, what version of glibc do you have?
Thanks,
Mark
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