On Apr 8, 2011, at 5:10 AM, NeilBrown wrote: > When a device gives a hard read error md/raid always calculates the correct > data from other devices (Assuming that parity is correct) and writes it out. > It does this for check and for repair and for normal IO. > > I am no expert on SMART however if there are no reallocated sectors then > maybe what happened is that whenever md wrote to a bad sector, the drive > determined that the media there was still usable and wrote the data there. > But that is just a guess. > excellent, thanks. this probably explains why the errors seem to be migrating around the disk - perhaps the ones that are getting corrected/rewritten are effectively being 'refreshed' and sectors that are sitting around unread for a while are rotting. i ran another check, and this time saw several read errors on one of the bad disks, but not on the other. strangely, i did not see raid correcting these sectors. i wonder if this means they eventually returned good data. does md/raid try more than once in the face of a hard error before correcting from parity? given that i have backups, i decided to just fail out the disk that was still giving errors. the raid is rebuilding now, and in 20h or so i'll know if i'm out of the woods. i think i'll probably also replace the other flaky disk, even though it's SMART status now looks pretty clean. === update: bad news... a *different* drive in the array threw a read error while rebuilding. i wonder if my controller or enclosure might be bad, since 3 out of 4 disks have exhibited random problems (and no reallocated sectors). anyway, now the raid is up, but in a degraded state. what i want to do is bring the array back to a clean state with 3 drives and restart the rebuild onto the new disk and see what happens. how do i get the "failed" disk back into "active sync" state? mdadm --manage /dev/md1 --add /dev/sdi1 returns "device busy", and --assemble won't take --assume-clean as an argument. do i have to stop and re-start the array? a little scared to do that. thanks, rob -- 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
