Hi! > 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 > May be I'm wrong, but this will not guarantee choice of different datacenters for n-1 and remaining replica. I have experimented with rules like this, trying to put one replica to "main host" and other replicas to some other hosts. Some OSDs was referenced two times in some of generated pg's. Pavel. > 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 > _______________________________________________ > ceph-users mailing list > ceph-users at lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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