Grow: print useful error when converting RAID1->RAID5 will fail.

RAID1 can only be converted to RAID0 or RAID5 if the size is
a multiple of 4K as we cannot have chunks smaller than 4K.

If this might happen, report a useful error message.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/Grow.c b/Grow.c
index a0dbb20..e3ef8d4 100644
--- a/Grow.c
+++ b/Grow.c
@@ -1023,6 +1023,10 @@ char *analyse_change(struct mdinfo *info, struct reshape *re)
 		 * raid5 with 2 disks, or
 		 * raid0 with 1 disk
 		 */
+		if (info->new_level > 1 &&
+		    (info->component_size & 7))
+			return "Cannot convert RAID1 of this size - "
+				"reduce size to multiple of 4K first.";
 		if (info->new_level == 0) {
 			if (info->delta_disks != UnSet &&
 			    info->delta_disks != 0)