On 08/04/2014 03:28 PM, Chris Kitzmiller wrote:
On Aug 1, 2014, at 1:31 PM, Mariusz Gronczewski wrote:
I got weird stalling during writes, sometimes I got same write speed
for few minutes and after some time it starts stalling with 0 MB/s for
minutes
I'm getting very similar behavior on my cluster. My writes start well but then just kinda
stop for a while and then bump along slowly until the bench finishes. I've got a thread
about it going here called "Ceph runs great then falters".
This kind of behaviour often results when the journal can write much
faster than the OSD data disks. Initially the journals will be able to
absorb the data and things will run along well, but eventually ceph will
need to stall writes if things get too out of sync. You may want to
take a look at what's happening on the data disks during your tests to
see if there's anything that looks suspect. Checking the admin socket
for dump_historic_ops might provide some clues as well.
Mark
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