On Thu, May 05, 2011 at 09:45:38AM +1000, NeilBrown wrote: > On Thu, 5 May 2011 00:08:59 +0100 Liam Kurmos <quantum.leaf@xxxxxxxxx> wrote: > > > as a separate question, what should be the theoretical performance of raid5? > > x(N-1) > > So a 4 drive RAID5 should read at 3 time the speed of a single drive. Actually, theoretically, it should be more than that for reading, more like N minus some overhead. In a raid5 stripe of 4 disks, when reading you do not read the checksum block, and thus you should be able to have all 4 drives occupied with reading real data. Some benchmarks back this up, http://home.comcast.net/~jpiszcz/20080329-raid/ http://blog.jamponi.net/2008/07/raid56-and-10-benchmarks-on-26255_10.html The latter reports a 3.44 times performance for raid5 reads with 4 disks, significantly over the N-1 = 3.0 mark. For writing, you are correct with the N-1 formular. best regards keld -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
