On Fri, Aug 29, 2014 at 12:52 AM, pragya jain <prag_2...@yahoo.co.in> wrote: > #2: why odd no. of monitors are recommended for production cluster, not even > no.?
Because to achieve a quorum, you must always have participation of more than 50% of the monitors. Not 50%. More than 50%. With an even number of monitors, half is not a quorum so you need half + 1. With an odd number of monitors, there's no such thing as half. So with an even number of monitors, one is always "wasted." 1 monitors -> 1 to make quorum -> 0 can be lost 2 monitors -> 2 to make quorum -> 0 can be lost 3 monitors -> 2 to make quorum -> 1 can be lost 4 monitors -> 3 to make quorum -> 1 can be lost 5 monitors -> 3 to make quorum -> 2 can be lost 6 monitors -> 4 to make quorum -> 2 can be lost 7 monitors -> 4 to make quorum -> 3 can be lost So an even number N of monitors doesn't give you any better fault resilience than N-1 monitors. And the more monitors you have, the more traffic there is between them. So when N is even, N monitors consume more resources and provide no extra benefit compared to N-1 monitors. Hope that helps! _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
