dm raid: add region_size parameter

Allow the user to specify the region_size.

Ensures that the supplied value meets md's constraints, viz. the number of
regions does not exceed 2^21.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt
index 4f9dd3cecc11..be4419a30781 100644
--- a/Documentation/device-mapper/dm-raid.txt
+++ b/Documentation/device-mapper/dm-raid.txt
@@ -52,6 +52,10 @@ The target is named "raid" and it accepts the following parameters:
         [max_recovery_rate <kB/sec/disk>]  Throttle RAID initialization
         [max_write_behind <sectors>]       See '-write-behind=' (man mdadm)
         [stripe_cache <sectors>]           Stripe cache size (higher RAIDs only)
+        [region_size <sectors>]
+                The region_size multiplied by the number of regions is the
+                logical size of the array.  The bitmap records the device
+                synchronisation state for each region.
 
 <#raid_devs>: The number of devices composing the array.
         Each device consists of two entries.  The first is the device