On Wed, May 14, 2014 at 9:56 AM, Fabrizio G. Ventola <fabrizio.ventola at uniba.it> wrote: > Hi everybody, > > Is it possible with CRUSH map to make a rule that puts R-1 replicas on > a node and the remaining one on a different node of the same failure > domain (for example datacenter) putting the replicas considering a > deeper failure domain (e.g. room)? Statement "step emit" may help in > this? > Ideally I'm trying to put two of three replicas into same datacenter > but in different rooms (or similar) and the remaining one in another > datacenter. CRUSH map can do this or it's only achievable with > zone/region configuration with rados gw? CRUSH can do this. You'd have two choose <bucket>...emit sequences; the first of which would descend down to a host and then choose n-1 devices within the host; the second would descend once. I think something like this should work: step take default step choose firstn 1 datacenter step chooseleaf firstn -1 room step emit step chooseleaf firstn 1 datacenter step emit Would pick one datacenter, and put R-1 copies of the data in separate rooms. Then it would pick another datacenter and put 1 copy of the data somewhere in it. I haven't tested this and it's been a while so there might be some sharp edges, though (I *think* that should work just fine, but you might need to use choose statements instead of chooseleaf all the way down or something). -Greg > And it's even possible to specifiy the "primary affinity" in the sense > that for specified clients (or for specified pools) ceph has to store > the primary replica in the closest (to the client) datacenter and the > other replica in another datacenter. To do something like this you'd want to set up pools with special rules to do that. Instead of "step take default" you'd do "step take <primary_datacenter>". -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com
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