[dm-devel] [PATCH] dm raid: don't allow "write behind" with raid4/5/6

[heinzm at redhat.com]

From: Heinz Mauelshagen <heinzm at redhat.com>

Only the md raid1 personality supports setting a maximum number
of "write behind" write ios on any legs set "write mostly".
"write mostly" enhances throughput with slow links/disks.

Technically the "write behind" value is a write intent bitmap
property only being respected by the raid1 personality. It allows
a maximum number of "write behind" writes to any "write mostly"
raid1 mirror legs to be delayed and reads from such legs avoided.

No other MD personalities supported via dm-raid types make
use of "write behind", thus setting this property is superfluous;
it wouldn't cause harm but it is correct to reject it.

Patch removes CTR_FLAG_MAX_WRITE_BEHIND from
raid4/5/6 valid flags allowed.

No bz is related, I came across it during review.

Signed-off-by: Heinz Mauelshagen <heinzm at redhat.com>
---
 drivers/md/dm-raid.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 698b03e..9d5c6bb 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -160,7 +160,6 @@ struct raid_dev {
 				 CTR_FLAG_DAEMON_SLEEP | \
 				 CTR_FLAG_MIN_RECOVERY_RATE | \
 				 CTR_FLAG_MAX_RECOVERY_RATE | \
-				 CTR_FLAG_MAX_WRITE_BEHIND | \
 				 CTR_FLAG_STRIPE_CACHE | \
 				 CTR_FLAG_REGION_SIZE | \
 				 CTR_FLAG_DELTA_DISKS | \
@@ -171,7 +170,6 @@ struct raid_dev {
 				 CTR_FLAG_DAEMON_SLEEP | \
 				 CTR_FLAG_MIN_RECOVERY_RATE | \
 				 CTR_FLAG_MAX_RECOVERY_RATE | \
-				 CTR_FLAG_MAX_WRITE_BEHIND | \
 				 CTR_FLAG_STRIPE_CACHE | \
 				 CTR_FLAG_REGION_SIZE | \
 				 CTR_FLAG_DELTA_DISKS | \
-- 
2.7.4