Ceph: Designing and Implementing Scalable Storage Systems

K+M

The more erasure code shards you have, the more OSD failures you can tolerate and still successfully read data. Likewise, the ratio of K to M shards each object is split into has a direct effect on the percentage of raw storage that is required for each object.

A 3+1 configuration will give you 75% usable capacity but only allows for a single OSD failure, and so would not be recommended. In comparison, a three-way replica pool only gives you 33% usable capacity.

4+2 configurations would give you 66% usable capacity and allows for two OSD failures. This is probably a good configuration for most people to use.

At the other end of the scale, 18+2 would give you 90% usable capacity and still allows for two OSD failures. On the surface this ...