[PATCH] md: optimise reconstruction when re-adding a recently failed drive.

When an array is degraded, bit in the intent-bitmap are never cleared.  So if
a recently failed drive is re-added, we only need to reconstruct the block
that are still reflected in the bitmap.

This patch adds support for this re-adding.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index c3b4772cfaea..3f5234fe3593 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -811,9 +811,12 @@ static int raid1_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
 {
         conf_t *conf = mddev->private;
         int found = 0;
-        int mirror;
+        int mirror = 0;
         mirror_info_t *p;
 
+        if (rdev->saved_raid_disk >= 0 &&
+            conf->mirrors[rdev->saved_raid_disk].rdev == NULL)
+                mirror = rdev->saved_raid_disk;
         for (mirror=0; mirror < mddev->raid_disks; mirror++)
                 if ( !(p=conf->mirrors+mirror)->rdev) {
 
@@ -830,6 +833,8 @@ static int raid1_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
                         p->head_position = 0;
                         rdev->raid_disk = mirror;
                         found = 1;
+                        if (rdev->saved_raid_disk != mirror)
+                                conf->fullsync = 1;
                         p->rdev = rdev;
                         break;
                 }