On Wed, 15 Feb 2017, Nick Fisk wrote: > Just an update. I spoke to Sage today and the general consensus is that > something like bcache or dmcache is probably the long term goal, but work > needs to be done before its ready for prime time. The current tiering > functionality won't be going away in the short term and not until there is a > solid replacement with bcache/dmcache/whatever. But from the sounds of it, > there won't be any core dev time allocated to it.
Quick clarification: I meant the cache tiering isn't going anywhere until there is another solid *rados* tiering replacement. The rados tiering plans will keep metadata in the base pool but link to data in one or more other (presumably colder) tiers (vs a sparse cache pool in front of the base pool). That is, you should consider rados tiering as totally orthogonal to tiering devices beneath a single OSD with dm-cache/bcache/flashcache. > I'm not really too bothered what the solution ends up being, but as we have > discussed the flexibility to shrink/grow the cache without having to > rebuild all your nodes/OSD's is a major, almost essential, benefit to me. Exactly. The new rados tiering approach would still provide this. > I've still got some ideas which I think can improve performance of the > tiering functionality, but unsure as to whether I have the coding skills to > pull it off. This might motivate me though to try and improve it in its > current form. FWIW the effectiveness of the existing rados cache tiering will also improve significantly with the EC overwrite support. Whether it is removed as part of a new/different rados tiering function in rados is really a function of how the code refactor works out and how difficult it is to support vs the use cases it covers that the new tiering does not. sage _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
