Great info! Many thanks! Tom
2015-03-25 13:30 GMT+01:00 Loic Dachary <l...@dachary.org>: > Hi Tom, > > On 25/03/2015 11:31, Tom Verdaat wrote:> Hi guys, > > > > We've got a very small Ceph cluster (3 hosts, 5 OSD's each for cold > data) that we intend to grow later on as more storage is needed. We would > very much like to use Erasure Coding for some pools but are facing some > challenges regarding the optimal initial profile “replication” settings > given the limited number of initial hosts that we can use to spread the > chunks. Could somebody please help me with the following questions? > > > > 1. > > > > Suppose we initially use replication in stead of erasure. Can we > convert a replicated pool to an erasure coded pool later on? > > What you would do is create an erasure coded pool later and have the > initial replicated pool as a cache in front of it. > > http://docs.ceph.com/docs/master/rados/operations/cache-tiering/ > > Objects from the replicated pool will move to the erasure coded pool if > they are not used and it will save space. You don't need to create the > erasure coded pool on your small cluster. You can do it when it grows > larger or when it becomes full. > > > 2. > > > > Will Ceph gain the ability to change the K and N values for an > existing pool in the near future? > > I don't think so. > > > 3. > > > > Can the failure domain be changed for an existing pool? E.g. can we > start with failure domain OSD and then switch it to Host after adding more > hosts? > > The failure domain, although listed in the erasure code profile for > convenience, really belongs to the crush ruleset applied to the pool. It > can therefore be changed after the pool is created. It is likely to result > in objects moving a lot during the transition but it should work fine > otherwise. > > > 4. > > > > Where can I find a good comparison of the available erasure code > plugins that allows me to properly decide which one suits are needs best? > > In a nutshell, jerasure is flexible and is likely to be what you want, isa > computes faster than jerasure but only works on intel processors (note > however that the erasure code computation does not make a significant > difference overall), lrc and shec (to be published in hammer) minimize > network usage during recovery but uses more space than jerasure or isa. > > Cheers > > > Many thanks for your help! > > > > Tom > > > > > > > > _______________________________________________ > > ceph-users mailing list > > ceph-users@lists.ceph.com > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > -- > Loïc Dachary, Artisan Logiciel Libre > >
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