> >> From reading the RBD layering docs it looked like you could also specify a > >> different object size for the target. If there was some way that the > >> snapshot could have a different object size or some sort of dirty bitmap, > >> then this would reduce the amount of data that would have to copied on > >> each > >> write. > > > > Have you tried using a different object size for your RBD image? I think > > your proposal is effectively the same as just reducing the object size > > (with the added overhead of a OSD<->client round-trip for CoW instead of > > handling it within the OSD directly). The default 4MB object size was an > > attempt to strike a balance between the CoW cost and the number of objects > > the OSDs would have to manage. > > Let's not overstate things: 4MB was chosen for RBD objects because > that's the size we use for objects in our cluster. That size comes > from the filesystem work Sage did at Santa Cruz and is not entirely > made up, but I don't think there was any kind of realistic testing nor > much in the way of numbers behind it. :) > -Greg > Sounds like a good performance test case for a production-ready BlueStore. -- Jason Dillaman _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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