[PATCH] md: Final stages of raid5 expand code

This patch adds raid5_reshape and end_reshape which will start and finish the
reshape processes.

raid5_reshape is only enabled in CONFIG_MD_RAID5_RESHAPE is set, to discourage
accidental use.

Read the 'help' for the CONFIG_MD_RAID5_RESHAPE entry.

and Make sure that you have backups, just in case.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index ac43f98062fd..fd2aae150ccc 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -127,6 +127,32 @@ config MD_RAID5
 
           If unsure, say Y.
 
+config MD_RAID5_RESHAPE
+        bool "Support adding drives to a raid-5 array (experimental)"
+        depends on MD_RAID5 && EXPERIMENTAL
+        ---help---
+          A RAID-5 set can be expanded by adding extra drives. This
+          requires "restriping" the array which means (almost) every
+          block must be written to a different place.
+
+          This option allows such restriping to be done while the array
+          is online.  However it is still EXPERIMENTAL code.  It should
+          work, but please be sure that you have backups.
+
+          You will need a version of mdadm newer than 2.3.1.   During the
+          early stage of reshape there is a critical section where live data
+          is being over-written.  A crash during this time needs extra care
+          for recovery.  The newer mdadm takes a copy of the data in the
+          critical section and will restore it, if necessary, after a crash.
+
+          The mdadm usage is e.g.
+               mdadm --grow /dev/md1 --raid-disks=6
+          to grow '/dev/md1' to having 6 disks.
+
+          Note: The array can only be expanded, not contracted.
+          There should be enough spares already present to make the new
+          array workable.
+
 config MD_RAID6
         tristate "RAID-6 mode"
         depends on BLK_DEV_MD