I was just looking at our crush rules as we need to change them from
failure domain host to failure domain datacenter. The replicated ones
seem trivial but what about this one for EC 4+2?
rule rbd_ec_data {
id 0
type erasure
step set_chooseleaf_tries 5
step set_choose_tries 100
step take default class hdd
step chooseleaf indep 0 type host
step emit
}
We already have this crush rule for EC 4+5:
"
rule cephfs.hdd.data {
id 7
type erasure
step set_chooseleaf_tries 5
step set_choose_tries 100
step take default class hdd
step choose indep 0 type datacenter
step chooseleaf indep 3 type host
step emit
}
"
I don't understand the "num" argument for the choose step. The
documentation[1] says:
"
If {num} == 0, choose pool-num-replicas buckets (as many buckets as are
available).
If pool-num-replicas > {num} > 0, choose that many buckets.
If {num} < 0, choose pool-num-replicas - {num} buckets.
"
Num is 0 but it's not replicated so how does this translate to picking 3
of 3 datacenters?
I am thinking we should just change 3 to 2 for the chooseleaf line for
the 4+2 rule since for 4+5 each DC needs 3 shards and for 4+2 each DC
needs 2 shards. Comments?
Mvh.
Torkil
[1] https://docs.ceph.com/en/reef/rados/operations/crush-map-edits/
--
Torkil Svensgaard
Systems Administrator
Danish Research Centre for Magnetic Resonance DRCMR, Section 714
Copenhagen University Hospital Amager and Hvidovre
Kettegaard Allé 30, 2650 Hvidovre, Denmark
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