Hi all, I have found on the mailing list that it should be possible to have a multi datacenter setup, if latency is low enough.
I would like to set this up, so that each datacenter has at least two replicas and each PG has a replication level of 3. In this <http://thread.gmane.org/gmane.comp.file-systems.ceph.user/2184/focus=2189> mail, it is suggested that I should use the following crush map for multi DC: rule dc { ruleset 0 type replicated min_size 1 max_size 10 step take default step chooseleaf firstn 0 type datacenter step emit } This looks suspicious to me, as it will only generate a list of two PG's, (and only one PG if one DC is down). I think I should use: rule replicated_ruleset { ruleset 0 type replicated min_size 1 max_size 10 step take root step choose firstn 2 type datacenter step chooseleaf firstn 2 type host step emit step take root step chooseleaf firstn -4 type host step emit } This correctly generates a list with 2 PG's in one DC, then 2 PG's in the other and then a list of PG's The problem is that this list contains duplicates (e.g. for 8 OSDS per DC) [*13*,*11*,1,8,*13*,*11*,16,4,3,7] [9,2,13,11,9,15,12,18,3,5] [3,5,17,10,3,5,7,13,18,10] [7,6,11,14,7,14,3,16,4,11] [6,3,15,18,6,3,12,9,16,15] Will this be a problem? If crush is executed, will it only consider osd's which are (up,in) or all OSD's in the map and then filter them from the list afterwards? Thx, Wouter
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