[PATCH] md: Allow the write_mostly flag to be set via sysfs

It appears in /sys/mdX/md/dev-YYY/state
and can be set or cleared by writing 'writemostly' or '-writemostly'
respectively.

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, 5 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index f3d418ba625e..0668f9dc9d29 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -309,6 +309,9 @@ Each directory contains:
               faulty   - device has been kicked from active use due to
                          a detected fault
               in_sync  - device is a fully in-sync member of the array
+              writemostly - device will only be subject to read
+                         requests if there are no other options.
+                         This applies only to raid1 arrays.
               spare    - device is working, but not a full member.
                          This includes spares that are in the process
                          of being recoverred to
@@ -316,6 +319,8 @@ Each directory contains:
         This can be written to.
         Writing "faulty"  simulates a failure on the device.
         Writing "remove" removes the device from the array.
+        Writing "writemostly" sets the writemostly flag.
+        Writing "-writemostly" clears the writemostly flag.
 
       errors
         An approximate count of read errors that have been detected on