With btrfs, we can't really put the log on a separate device. What we
can do however is mirror the metadata across two devices and put the
data on a single device. When we turn on dmerror then the metadata can
fall back to using the other mirror while the data errors out.

Signed-off-by: Jeff Layton <redacted>
---
 common/rc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/common/rc b/common/rc
index 8b815d9c8c33..2084c1f24f30 100644
--- a/common/rc
+++ b/common/rc

@@ -829,6 +829,8 @@ _scratch_mkfs()
 		;;
 	btrfs)
 		mkfs_cmd="$MKFS_BTRFS_PROG"
+		[ "$USE_EXTERNAL" = yes -a ! -z "$SCRATCH_LOGDEV" ] && \
+			mkfs_cmd="$mkfs_cmd -d single -m raid1 $SCRATCH_LOGDEV"
 		mkfs_filter="cat"
 		;;
 	ext2|ext3)

-- 
2.9.3