Hi Erik, On 15/08/2014 11:54, Erik Logtenberg wrote: > Hi, > > With EC pools in Ceph you are free to choose any K and M parameters you > like. The documentation explains what K and M do, so far so good. > > Now, there are certain combinations of K and M that appear to have more > or less the same result. Do any of these combinations have pro's and > con's that I should consider and/or are there best practices for > choosing the right K/M-parameters? > > For instance, if I choose K = 3 and M = 2, then pg's in this pool will > use 5 OSD's and sustain the loss of 2 OSD's. There is 40% overhead in > this configuration. > > Now, if I were to choose K = 6 and M = 4, I would end up with pg's that > use 10 OSD's and sustain the loss of 4 OSD's, which is statistically not > so much different from the first configuration. Also there is the same > 40% overhead.
Although I don't have numbers in mind, I think the odds of loosing two OSD simultaneously are a lot smaller than the odds of loosing four OSD simultaneously. Or am I misunderstanding you when you write "statistically not so much different from the first configuration" ? Cheers > One rather obvious difference between the two configurations is that the > latter requires a cluster with at least 10 OSD's to make sense. But > let's say we have such a cluster, which of the two configurations would > be recommended, and why? > > Thanks, > > Erik. > _______________________________________________ > 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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