Hi all, Whilst on a training course recently I was told that 'min_size' had an affect on client write performance, in that it's the required number of copies before ceph reports back to the client that an object has been written therefore setting a 'min_size' of 0 would only require a write to be accepted by the journal before confirming it's been accepted.
This is contrary to further reading elsewhere that the 'min_size' is the minimum number of copies required of an object to allow I/O and that 'size' is the parameter that would affect write speed i.e. desired number of replicas. Setting 'min_size' to 0 with a 'size' of 3 you would still have an effective 'min_size' of 2 from: https://raw.githubusercontent.com/ceph/ceph/master/doc/release-notes.rst "* Degraded mode (when there fewer than the desired number of replicas) is now more configurable on a per-pool basis, with the min_size parameter. By default, with min_size 0, this allows I/O to objects with N - floor(N/2) replicas, where N is the total number of expected copies. Argonaut behavior was equivalent to having min_size = 1, so I/O would always be possible if any completely up to date copy remained. min_size = 1 could result in lower overall availability in certain cases, such as flapping network partition" Which leads to the conclusion that changing 'min_size' has nothing to do with performance but is solely related to data integrity/resilience. Could someone confirm my assertion is correct? Many thanks James _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
