On Mon, Aug 22, 2011 at 11:58 PM, NeilBrown <neilb@xxxxxxx> wrote: > More concrete details would help... Sorry, you're right, I though it could have been something fast. I have details for the first test I made with 15 RAIDs. > > So you have 8 MD RAID1s each with one missing device and the other device is > the next RAID1 down in the stack, except that last RAID1 where the one device > is a real device. Exactly, only 1 real device at the moment. > > And in some unspecified test the RAID1 at the top of the stack gives 2/3 the > performance of the plain device? This the same when all bitmaps are > removed. > > Certainly seems strange. > > Can you give details of the test and numbers etc. So the test is a backup, Veeam exactly, using Samba 3.6.0 with brand new SMB2 protocol, bitmaps are removed. The backup took 45 minutes instead of 14 to 22 minutes. Here is a sample of iostat showing the average queue size increasing by RAID devices: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util sdb 0.00 35.67 0.00 27.00 0.00 5579.00 413.26 2.01 74.69 0.00 74.69 34.32 92.67 md64 0.00 0.00 0.00 61.33 0.00 5577.00 181.86 0.00 0.00 0.00 0.00 0.00 0.00 md65 0.00 0.00 0.00 60.00 0.00 5574.67 185.82 0.00 0.00 0.00 0.00 0.00 0.00 md66 0.00 0.00 0.00 58.67 0.00 5572.33 189.97 0.00 0.00 0.00 0.00 0.00 0.00 md67 0.00 0.00 0.00 58.67 0.00 5572.33 189.97 0.00 0.00 0.00 0.00 0.00 0.00 md68 0.00 0.00 0.00 58.67 0.00 5572.33 189.97 0.00 0.00 0.00 0.00 0.00 0.00 md69 0.00 0.00 0.00 58.67 0.00 5572.33 189.97 0.00 0.00 0.00 0.00 0.00 0.00 md70 0.00 0.00 0.00 58.33 0.00 5572.00 191.04 0.00 0.00 0.00 0.00 0.00 0.00 md71 0.00 0.00 0.00 57.00 0.00 5569.67 195.43 0.00 0.00 0.00 0.00 0.00 0.00 md72 0.00 0.00 0.00 55.67 0.00 5567.33 200.02 0.00 0.00 0.00 0.00 0.00 0.00 md73 0.00 0.00 0.00 54.33 0.00 5565.00 204.85 0.00 0.00 0.00 0.00 0.00 0.00 md74 0.00 0.00 0.00 53.00 0.00 5562.67 209.91 0.00 0.00 0.00 0.00 0.00 0.00 md75 0.00 0.00 0.00 51.67 0.00 5560.33 215.24 0.00 0.00 0.00 0.00 0.00 0.00 md76 0.00 0.00 0.00 50.33 0.00 5558.00 220.85 0.00 0.00 0.00 0.00 0.00 0.00 md77 0.00 0.00 0.00 49.00 0.00 5555.67 226.76 0.00 0.00 0.00 0.00 0.00 0.00 md78 0.00 0.00 0.00 47.67 0.00 5553.33 233.01 0.00 0.00 0.00 0.00 0.00 0.00 -- 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
