On Wed, 04 Mar 2015 12:55:43 -0700 Eric Mei <meijia@xxxxxxxxx> wrote:
> Hi,
>
> It is interesting to notice that RAID1 won't mark the last working drive
> as Faulty no matter what. The responsible code seems here:
>
> static void error(struct mddev *mddev, struct md_rdev *rdev)
> {
> ...
> /*
> * If it is not operational, then we have already marked it as dead
> * else if it is the last working disks, ignore the error, let the
> * next level up know.
> * else mark the drive as failed
> */
> if (test_bit(In_sync, &rdev->flags)
> && (conf->raid_disks - mddev->degraded) == 1) {
> /*
> * Don't fail the drive, act as though we were just a
> * normal single drive.
> * However don't try a recovery from this drive as
> * it is very likely to fail.
> */
> conf->recovery_disabled = mddev->recovery_disabled;
> return;
> }
> ...
> }
>
> The end result is that even if all the drives are physically gone, there
> still one drive remains in array forever, and mdadm continues to report
> the array is degraded instead of failed. RAID10 also has similar behavior.
>
> Is there any reason we absolutely don't want to fail the last drive of
> RAID1?
>
When a RAID1 only has one drive remaining, then it should act as much as
possible like a single plain ordinary drive.
How does /dev/sda behave when you physically remove the device? md0 (as a
raid1 with one drive) should do the same.
NeilBrown
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