Re: Unexpectedly slow write performance (RBD cinder volumes)

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On Thu, Aug 22, 2013 at 2:47 PM, Oliver Daudey <oliver@xxxxxxxxx> wrote:
> Hey Greg,
>
> Thanks for the tip!  I was assuming a clean shutdown of the OSD should
> flush the journal for you and have the OSD try to exit with it's
> data-store in a clean state?  Otherwise, I would first have to stop
> updates a that particular OSD, then flush the journal, then stop it?

Nope, clean shutdown doesn't force a flush as it could potentially
block on the filesystem. --flush-journal is a CLI option, so you would
turn off the OSD, then run it with that option (it won't join the
cluster or anything, just look at and update local disk state), then
downgrade the binary.
In all likelihood this won't have caused you to lose any data because
in many/most situations the OSD actually will have written out
everything in the journal to the local FS before you tell it to shut
down, and as long as one of the other OSDs either did that or turned
back on without crashing then it will propagate the newer updates to
everybody. But wiping the journal without flushing is certainly not
the sort of thing you should get in the habit of doing.
-Greg
Software Engineer #42 @ http://inktank.com | http://ceph.com
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