Following last week article, here is another CRUSH example. This time we want to store our first replica on SSD drives and the second copy on SATA drives.

Here is the CRUSH rule:

rule ssd-primary-affinity {
    ruleset 0
    type replicated
    min_size 2
    max_size 3
    step take ssd
    step chooseleaf firstn 1 type host
    step emit
    step take sata
    step chooseleaf firstn -1 type host
    step emit
}

Make sure that you configure your OSD with the primary affinty flag as well, for reference look at my article about primary affinity.