On Wed, 26 Nov 2014 05:37:43 -0600 Mark Nelson wrote: > On 11/26/2014 04:05 AM, Yujian Peng wrote: [snip] > > > > > Since the size of jornal partitions on SSDs is 10G, I want to set > > filestore max sync interval to 30 minutes. Is 30 minutes resonable? > > How to set filestore max sync interval on the fly? > > The effect of this is that you'll be able to write the journal > uninterrupted for a long time, but syncs could be very expensive. I'd > suggest giving it a try at a couple of values (default, 60s, 300s) under > say 20 minutes of continuous heavy workload to observe the effects and > see how you like it. > When I asked more or less the same question a while ago, I was left with the following information, please correct me if I'm wrong: 1. "filestore max sync interval" is the longest time one can write to the journal, but flushes to the backing store can and will happen a lot earlier than that. What triggers these besides what I'm going to list below was left rather vague, though. If you want to enforce long periods of journal usage before writing out and hopefully coalescing things a lot, one needs to raise "filestore min sync interval". And the warnings about expensive syncs go double when doing that. 2. Once the journal is half full, a flush is triggered in any case. And once the journals are on SSDs, Yujian will likely discover that now his CPUs are the bottleneck in certain situations. ^o^ As for setting things on the fly, look for the "injectargs" syntax, like: ceph tell osd.* injectargs '--filestore_max_sync_interval 30' Christian -- Christian Balzer Network/Systems Engineer chibi@xxxxxxx Global OnLine Japan/Fusion Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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