Le 13/11/2017 à 15:47, Oscar Segarra a écrit : > Thanks Mark, Peter, > > For clarification, the configuration with RAID5 is having many servers > (2 or more) with RAID5 and CEPH on top of it. Ceph will replicate data > between servers. Of course, each server will have just one OSD daemon > managing a big disk. > > It looks functionally is the same using RAID5 + 1 Ceph daemon as 8 > CEPH daemons. Functionally it's the same but RAID5 will kill your write performance. For example if you start with 3 OSD hosts and a pool size of 3, due to RAID5 each and every write on your Ceph cluster will imply a read on one server on every disks minus one then a write on *all* the disks of the cluster. If you use one OSD per disk you'll have a read on one disk only and a write on 3 disks only : you'll get approximately 8 times the IOPS for writes (with 8 disks per server). Clever RAID5 logic can minimize this for some I/O patterns but it is a bet and will never be as good as what you'll get with one disk per OSD. Best regards, Lionel _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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