On Dec 21, 2013 12:32 PM, "shacky" <shack...@gmail.com> wrote: >> >> I all depends on the replication level you use, but let's assume 3. > > > Does replication level 3 mean that the data are all replicated three times in the cluster? >
Replication is set on a per pool basis. You can set some, or all, pools to replica size of 2 instead of 3. >> So you get the capacity of one machine. >> >> 4 * 1000 * 1000 / 1024 /1024 = 3.81TB >> >> This would result in 15.24TB of raw space per machine, so 45TB of raw capacity in the cluster. >> >> You probably shouldn't fill the disks over 80% just to be safe. So with 3x replication you have 12.2TB of usable storage. > > > From 45TB to 12.2TB? So less? > I would expect something similar to RAID5 (about 36GB of usable storage). > I think I don't understand how Ceph works: could you help me to understand well? > Ceph uses replication not erasure coding (unlike RAID). So data is completely duplicated in multiple copies. Erasure coding is scheduled for the Firefly release, according to the roadmap. -JJ Galvez > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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