> Op 9 december 2016 om 22:31 schreef Oliver Humpage <[email protected]>: > > > > > On 7 Dec 2016, at 15:01, Wido den Hollander <[email protected]> wrote: > > > > I would always run with min_size = 2 and manually switch to min_size = 1 if > > the situation really requires it at that moment. > > Thanks for this thread, it’s been really useful. > > I might have misunderstood, but does min_size=2 also mean that writes have to > wait for at least 2 OSDs to have data written before the write is confirmed? > I always assumed this would have a noticeable effect on performance and so > left it at 1. > > Our use case is RBDs being exported as iSCSI for ESXi. OSDs are journalled on > enterprise SSDs, servers are linked with 10Gb, and we’re generally getting > very acceptable speeds. Any idea as to how upping min_size to 2 might affect > things, or should we just try it and see? >
As David already said, when all OSDs are up and in for a PG Ceph will wait for ALL OSDs to Ack the write. Writes in RADOS are always synchronous. Only when OSDs go down you need at least min_size OSDs up before writes or reads are accepted. So if min_size = 2 and size = 3 you need at least 2 OSDs online for I/O to take place. Wido > Oliver. > > _______________________________________________ > ceph-users mailing list > [email protected] > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
