We are using Hammer - latest released version. How do I check if it's getting promoted into the cache?
We're using the latest ceph kernel client. Where do I poke at readahead settings there? On Tue, Sep 8, 2015 at 8:29 AM, Gregory Farnum <gfar...@redhat.com> wrote: > On Thu, Sep 3, 2015 at 11:58 PM, Kyle Hutson <kylehut...@ksu.edu> wrote: > > I was wondering if anybody could give me some insight as to how CephFS > does > > its caching - read-caching in particular. > > > > We are using CephFS with an EC pool on the backend with a replicated > cache > > pool in front of it. We're seeing some very slow read times. Trying to > > compute an md5sum on a 15GB file twice in a row (so it should be in > cache) > > takes the time from 23 minutes down to 17 minutes, but this is over a > 10Gbps > > network and with a crap-ton of OSDs (over 300), so I would expect it to > be > > down in the 2-3 minute range. > > A single sequential read won't necessarily promote an object into the > cache pool (although if you're using Hammer I think it will), so you > want to check if it's actually getting promoted into the cache before > assuming that's happened. > > > > > I'm just trying to figure out what we can do to increase the > performance. I > > have over 300 TB of live data that I have to be careful with, though, so > I > > have to have some level of caution. > > > > Is there some other caching we can do (client-side or server-side) that > > might give us a decent performance boost? > > Which client are you using for this testing? Have you looked at the > readahead settings? That's usually the big one; if you're only asking > for 4KB at once then stuff is going to be slow no matter what (a > single IO takes at minimum about 2 milliseconds right now, although > the RADOS team is working to improve that). > -Greg > > > > > _______________________________________________ > > ceph-users mailing list > > ceph-users@lists.ceph.com > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > >
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