Keld Jørn Simonsen said: (by the date of Thu, 31 Jan 2008 02:55:07 +0100) > Given that you want maximum thruput for both reading and writing, I > think there is only one way to go, that is raid0. > > All the raid10's will have double time for writing, and raid5 and raid6 > will also have double or triple writing times, given that you can do > striped writes on the raid0. > > For random and sequential writing in the normal case (no faulty disks) I would > guess that all of the raid10's, the raid1 and raid5 are about equally fast, given the > same amount of hardware. (raid5, raid6 a little slower given the > unactive parity chunks). > > For random reading, raid0, raid1, raid10 should be equally fast, with > raid5 a little slower, due to one of the disks virtually out of > operation, as it is used for the XOR parity chunks. raid6 should be > somewhat slower due to 2 non-operationable disks. raid10,f2 may have a > slight edge due to virtually only using half the disk giving better > average seek time, and using the faster outer disk halves. > > For sequential reading, raid0 and raid10,f2 should be equally fast. > Possibly raid10,o2 comes quite close. My guess is that raid5 then is > next, achieving striping rates, but with the loss of one parity drive, > and then raid1 and raid10,n2 with equal performance. > > In degraded mode, I guess for random read/writes the difference is not > big between any of the raid1, raid5 and raid10 layouts, while sequential > reads will be especially bad for raid10,f2 approaching the random read > rate, and others will enjoy the normal speed of the above filesystem > (ext3, reiserfs, xfs etc). Wow! Thanks for detailed explanations. I was thinking that maybe raid10 on 4 drives could be faster than raid0. But now it's all logical for me. With 4 drives and raid10,f2 I could get an "extra" reading speed, but not the writing speed. Makes a lot of sense. Perhaps it should be added to linux-raid wiki? (and perhaps a FAQ there - isn't a question about speed a frequent one?) http://linux-raid.osdl.org/index.php/Main_Page > Theory, theory theory. Show me some real figures. yes... that would be great if someone could spend some time benchmarking all possible configurations :-) thanks for your help! -- Janek Kozicki - 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
