[PATCH] md: support stripe/offset mode in raid10
The "industry standard" DDF format allows for a stripe/offset layout where
data is duplicated on different stripes. e.g.
A B C D
D A B C
E F G H
H E F G
(columns are drives, rows are stripes, LETTERS are chunks of data).
This is similar to raid10's 'far' mode, but not quite the same. So enhance
'far' mode with a 'far/offset' option which follows the layout of DDFs
stripe/offset.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/raid/raid10.h b/include/linux/raid/raid10.h
index b110329..c41e56a 100644
--- a/include/linux/raid/raid10.h
+++ b/include/linux/raid/raid10.h
@@ -24,11 +24,16 @@
int far_copies; /* number of copies layed out
* at large strides across drives
*/
+ int far_offset; /* far_copies are offset by 1 stripe
+ * instead of many
+ */
int copies; /* near_copies * far_copies.
* must be <= raid_disks
*/
sector_t stride; /* distance between far copies.
- * This is size / far_copies
+ * This is size / far_copies unless
+ * far_offset, in which case it is
+ * 1 stripe.
*/
int chunk_shift; /* shift from chunks to sectors */