On Wednesday June 4, hubskml@xxxxxxx wrote: > Hello > > According to mdadm's man page: > "When creating a RAID5 array, mdadm will automatically create a degraded > array with an extra spare drive. This is because building the spare > into a degraded array is in general faster than resyncing the parity on > a non-degraded, but not clean, array. This feature can be over-ridden > with the --force option." > > Unfortunately, I'm seeing a kind of bug when I create a RAID5 array with > an internal bitmap, then stop the array before the initial > synchronization is done and restart the array. > > 1° When I create the array with an internal bitmap: > mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -b internal -R /dev/sd? > I see the last disk as a spare disk. After the restart of the array, all > disks are seen active and the array is not continuing the aborted > synchronization! > Note that I did not use the --assume-clean option. > > 2° When I create the array without a bitmap: > mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -R /dev/sd? > I see the last disk as a spare disk. After the restart of the array, the > spare disk is still a spare disk and the array continues the > synchronization where it had stopped. > > In the case 1°, is this a bug or did I miss something? Thanks for the detailed report. Yes, this is a bug. The following patch fixes it, though I'm not 100% sure this is the right fix (it may cause too much resync in some cases, which is better than not enough, but not ideal). > Secondly, what could be the consequences of this non-performed > synchronization ? If you lose a drive, the data might get corrupted. When writing to the array, the new parity block will sometimes be calculated assuming that it was previously correct. If all updates to a particular parity block are of this sort, then it will still be incorrect when you lose a drive, and data recovered based on that parity block will be incorrect. Until you lose a drive, it will have no visible effect. NeilBrown Signed-off-by: Neil Brown <neilb@xxxxxxx> diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c --- .prev/drivers/md/raid5.c 2008-06-10 10:27:51.000000000 +1000 +++ ./drivers/md/raid5.c 2008-06-12 09:34:25.000000000 +1000 @@ -4094,7 +4094,9 @@ static int run(mddev_t *mddev) " disk %d\n", bdevname(rdev->bdev,b), raid_disk); working_disks++; - } + } else + /* Cannot rely on bitmap to complete recovery */ + conf->fullsync = 1; } /* -- 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
