I have a cluster of 3 hosts each with 2 SSD and 4 Spinning disks.
I used the example in th ecrush map doco to create a crush map to place
the primary on the SSD and replica on spinning disk.
If I use the example, I end up with objects replicated on the same host,
if I use 2 replicas.
Question 1, is the documentation on the rules correct, should they
really be both ruleset 4 and why? I used ruleset 5 for the ssd-primary.
rule ssd {
ruleset 4
type replicated
min_size 0
max_size 10
step take ssd
step chooseleaf firstn 0 type host
step emit
}
rule ssd-primary {
ruleset 4
type replicated
min_size 0
max_size 10
step take ssd
step chooseleaf firstn 1 type host
step emit
step take platter
step chooseleaf firstn -1 type host
step emit
}
Question 2, Is there any way to ensure that the replicas are on
different hosts when we use double rooted trees for the 2 technologies?
Obviously, the simplest way is to have them on separate hosts.
For the moment, I have increased the number of replicas in the pool to 3
which does ensure that there is at least copies spread across multiple
hosts.
Darryl
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