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. 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.
 |