On Thursday May 14, rfu@xxxxxxxxxxxxxxxxxxxxxxxx wrote: > Hi guys, > > I'm a but confused about the duration of a raid5 resync: > > - occasionally, my server with 4*750 gb sata raid5 crashed (because of > problems with the power supply); after rebooting it took about 10 to 12 > hours to resync the raid5 (guess it just re-created some parity > information or however it works internally, but didn't have to copy > any data) A resync reads all the data and checks the parity. If it find bad parity (which is likely to be very rare) then it corrects it. So resync should run at the full speed of the hardware, just reading. > > - right now I replaced one 750GB disk with a 1.5TB disk, but now > resyncing (according to /proc/mdstat) it is supposed to take only 160 > minutes ?! although it needs top copy data to a blank disk ? > > is this normal or should I be worried, especially before I pull out > the next 750GB disk and replace it with the next 1.5TB disk ? recovery reads N-1 drives and writes the N'th drive. So it shuffles exactly the same amount of data as sync, and performs just as many IO operations, though some of them are writes rather than reads. I believe that (on rotating drives) writes go at much the same speed as reads. So you would expect this to take exactly as long as the resync. As others have said, 3 hours it a reasonable ball-part for 750Gig. 10-12 hours is definitely longer than I would expect. Of course, if use are using the array then resync (or recovery) will back off and let the regular IO have priority. So if you were actively using the array during the 10-12 hours resync, then it makes perfect sense. 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
