On 11/23/2013 11:14 PM, John Williams wrote: > On Sat, Nov 23, 2013 at 8:03 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: > >> Parity array rebuilds are read-modify-write operations. The main >> difference from normal operation RMWs is that the write is always to the >> same disk. As long as the stripe reads and chunk reconstruction outrun >> the write throughput then the rebuild speed should be as fast as a >> mirror rebuild. But this doesn't appear to be what people are >> experiencing. Parity rebuilds would seem to take much longer. > > "This" doesn't appear to be what SOME people, who have reported > issues, are experiencing. Their issues must be examined on a case by > case basis. Given what you state below this may very well be the case. > But I, and a number of other people I have talked to or corresponded > with, have had mdadm RAID 5 or RAID 6 rebuilds of one drive run at > approximately the optimal sequential write speed of the replacement > drive. It is not unusual on a reasonably configured system. I freely admit I may have drawn an incorrect conclusion about md parity rebuild performance based on incomplete data. I simply don't recall anyone stating here in ~3 years that their parity rebuilds were speedy, but quite the opposite. I guess it's possible that each one of those cases was due to another factor, such as user load, slow CPU, bus bottleneck, wonky disk firmware, backplane issues, etc. -- Stan -- 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
