Ok, thanks for the suggestions, I will try to achieve this in the next days and I will share my experience with you. Cheers, Fabrizio On 14 May 2014 20:12, Gregory Farnum <greg at inktank.com> wrote: > On Wed, May 14, 2014 at 10:52 AM, Pavel V. Kaygorodov <pasha at inasan.ru> wrote: >> 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. > > Argh, I forgot about this, but you're right. :( So you can construct > these sorts of systems manually (by having different "step take...step > emit" blocks, but CRUSH won't do it for you in a generic way. > > However, for *most* situations that people are interested in, you can > pull various tricks to accomplish what you're actually after. (I > haven't done this one myself, but I'm told others have.) For instance, > if you just want 1 copy segregated from the others, you can do this: > > step take default > step choose firstn 2 datacenter > step chooseleaf firstn -1 room > step emit > > That will generate an ordered list of 2(n-1) OSDs, but since you only > want n, you'll take n-1 from the first datacenter and only 1 from the > second. :) You can extend this to n-2, etc. > > If you have the pools associated with particular datacenters, you can > set up rules which place a certain number of copies in the primary > datacenter, and then use parallel crush maps to choose one of the > other datacenters for a given number of replica copies. (That is, you > can have multiple root buckets; one for each datacenter that includes > everybody BUT the datacenter it is associated with.) > -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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