On Mon, 22 Aug 2011 23:45:53 -0400 Jérôme Poulin <jeromepoulin@xxxxxxxxx> wrote: > On Mon, Aug 15, 2011 at 7:55 PM, NeilBrown <neilb@xxxxxxx> wrote: > > Yes, add another one later would be difficult. But if you know up-front that > > you will want three off-site devices it is easy. > > > > You could > > > > mdadm -C /dev/md0 -l1 -n2 -b internal /dev/A missing > > mdadm -C /dev/md1 -l1 -n2 -b internal /dev/md0 missing > > mdadm -C /dev/md2 -l1 -n2 -b internal /dev/md1 missing > > mdadm -C /dev/md3 -l1 -n2 -b internal /dev/md2 missing > > > > mkfs /dev/md3 ; mount .. > > > > So you now have 4 "missing" devices. > > Alright, so I tried that on my project, being a low-end device is > resulted in about 30-40% performance lost with 8 MDs (planning in > advance), I tried disabling all bitmap to see if it helps and I get > minimal performance gain. Is there anything I should tune in this > case? More concrete details would help... 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. 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. NeilBrown -- 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
