md: restore ability of spare drives to spin down.
authorNeilBrown <neilb@suse.de>
Fri, 7 May 2010 09:44:26 +0000 (19:44 +1000)
committerNeilBrown <neilb@suse.de>
Tue, 18 May 2010 05:28:00 +0000 (15:28 +1000)
commit75a73a29e520a6ce982b0da6dd8b7560ae3faa90
tree1bcb14b69e2ae7673bf29be6b3f27aee6e896070
parentaf3a2cd6b8a479345786e7fe5e199ad2f6240e56
md: restore ability of spare drives to spin down.

Some time ago we stopped the clean/active metadata updates
from being written to a 'spare' device in most cases so that
it could spin down and say spun down.  Device failure/removal
etc are still recorded on spares.

However commit 51d5668cb2e3fd1827a55 broke this 50% of the time,
depending on whether the event count is even or odd.
The change log entry said:

   This means that the alignment between 'odd/even' and
    'clean/dirty' might take a little longer to attain,

how ever the code makes no attempt to create that alignment, so it
could take arbitrarily long.

So when we find that clean/dirty is not aligned with odd/even,
force a second metadata-update immediately.  There are already cases
where a second metadata-update is needed immediately (e.g. when a
device fails during the metadata update).  We just piggy-back on that.

Reported-by: Joe Bryant <tenminjoe@yahoo.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
drivers/md/md.c