dm cache: document metadata device is exclussive to a cache

A cache's metadata device may not be shared by multiple cache devices.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>

diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt
index e8cdf7241b66b3b413b0253042b4d4a54700dc4e..af99c458c841dd248b443ad0ac74cacc8657614e 100644 (file)
--- a/Documentation/device-mapper/cache.txt
+++ b/Documentation/device-mapper/cache.txt
@@ -50,7 +50,8 @@ other parameters detailed later):
    which are dirty, and extra hints for use by the policy object.
    This information could be put on the cache device, but having it
    separate allows the volume manager to configure it differently,
-   e.g. as a mirror for extra robustness.
+   e.g. as a mirror for extra robustness.  This metadata device may only
+   be used by a single cache device.
 
 Fixed block size
 ----------------