On Sat, 8 Feb 2014, Christian Balzer wrote: > On Fri, 07 Feb 2014 18:46:31 +0100 Christian Kauhaus wrote: > > > Am 07.02.2014 14:42, schrieb Mark Nelson: > > > Ok, so the reason I was wondering about the use case is if you were > > > doing RBD specifically. Fragmentation has been something we've > > > periodically kind of battled with but still see in some cases. BTRFS > > > especially can get pretty spectacularly fragmented due to COW and > > > overwrites. There's a thread from a couple of weeks ago called "rados > > > io hints" that you may want to look at/contribute to. > > > > Thank you for the hint. Sage's proposal on ceph-devel sounds good, so > > I'll wait for an implementation. > > > > Pardon me for stating the maybe painfully obvious, but wouldn't setting the > allocsize to 4MB (with XFS and the default Ceph object size) do a world of > good to prevent fragmentation? This is what we plan on doing, although I was thinking an allocation size of 1MB might be more appropriate as a default. In any case, though, the challenge is that not all objects are RBD objects, nor are all images using 4MB objects, so the OSD can't blindly do this; it needs to respond to a hint from the client. Ilya is working on this now. sage _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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