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[PATCH] md: avoid backward event updates in md superblock when degraded.

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If we
  - shut down a clean array,
  - restart with one (or more) drive(s) missing
  - make some changes
  - pause, so that they array gets marked 'clean',
the event count on the superblock of included drives
will be the same as that of the removed drives.
So adding the removed drive back in will cause it
to be included with no resync.

To avoid this, we only update the eventcount backwards when the array
is not degraded.  In this case there can (should) be no non-connected
drives that we can get confused with, and this is the particular case
where updating-backwards is valuable.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
NeilBrown 2006-08-27 01:23:49 -07:00 committed by Linus Torvalds
parent 45f17e0c2a
commit 8469219596
1 changed files with 13 additions and 0 deletions
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13
drivers/md/md.c
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@ -1597,6 +1597,19 @@ void md_update_sb(mddev_t * mddev)
repeat:
spin_lock_irq(&mddev->write_lock);
if (mddev->degraded && mddev->sb_dirty == 3)
/* If the array is degraded, then skipping spares is both
* dangerous and fairly pointless.
* Dangerous because a device that was removed from the array
* might have a event_count that still looks up-to-date,
* so it can be re-added without a resync.
* Pointless because if there are any spares to skip,
* then a recovery will happen and soon that array won't
* be degraded any more and the spare can go back to sleep then.
*/
mddev->sb_dirty = 1;
sync_req = mddev->in_sync;
mddev->utime = get_seconds();
if (mddev->sb_dirty == 3)