On Wed, Sep 9, 2015 at 9:34 AM, Gregory Farnum <gfar...@redhat.com> wrote:
> On Wed, Sep 9, 2015 at 3:27 PM, Kyle Hutson <kylehut...@ksu.edu> wrote: > > We are using Hammer - latest released version. How do I check if it's > > getting promoted into the cache? > > Umm...that's a good question. You can run rados ls on the cache pool, > but that's not exactly scalable; you can turn up logging and dig into > them to see if redirects are happening, or watch the OSD operations > happening via the admin socket. But I don't know if there's a good > interface for users to just query the cache state of a single object. > :/ > even using 'rados ls', I (naturally) get cephfs object names - is there a way to see a filename -> objectname conversion ... or objectname -> filename ? > > We're using the latest ceph kernel client. Where do I poke at readahead > > settings there? > > Just the standard kernel readahead settings; I'm not actually familiar > with how to configure those but I don't believe Ceph's are in any way > special. What do you mean by "latest ceph kernel client"; are you > running one of the developer testing kernels or something? No, just what comes with the latest stock kernel. Sorry for any confusion. > I think > Ilya might have mentioned some issues with readahead being > artificially blocked, but that might have only been with RBD. > > Oh, are the files you're using sparse? There was a bug with sparse > files not filling in pages that just got patched yesterday or > something. > No, these are not sparse files. Just really big. > > > > 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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