On Sun, May 8, 2011 at 8:04 PM, Simon Tian <aixt2006@xxxxxxxxx> wrote: > For primary copy, I think when the replication size is 3, 4, or even > more, the writing speed should also near with 2 replication. Because > the 2nd, 3rd, 4th, ... replication are written parallelly. The speed > I got for 3, 4 replication is not near with the speed of 2, in fact, > like linear reduce. You're hitting your network limits there. With primary copy then the primary needs to send out the data to each of the replicas, which caps the write speed at (network bandwidth) / (num replicas). Presumably you're using a gigabit network (or at least your nodes have gigabit connections): 1 replica: ~125MB/s (really a bit less due to protocol overhead) 2 replicas:~62MB/s 3 replicas: ~40MB/s 4 replicas: ~31MB/s etc. Of course, you can also be limited by the speed of your disks (don't forget to take journaling into account); and your situation is further complicated by having multiple daemons per physical node. But I suspect you get the idea. :) -Greg -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
