manpage: add prompt in --zero-superblock against clustered raid

Clustered raid would be damaged if calls --zero-superblock
incorrectly, so add prompt in --zero-superblock chapter of
manpage. Such as: cluster node1 has assembled cluster-md,
but calls --zero-superblock in other cluster node.

Signed-off-by: Zhilong Liu <zlliu@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>

diff --git a/mdadm.8.in b/mdadm.8.in
index f0fd1fce7cbd587438ac91ed3e6d1367f239b62e..e6befeb03c1b37f5602de48de90b76b187a4728b 100644 (file)
--- a/mdadm.8.in
+++ b/mdadm.8.in
@@ -1691,6 +1691,10 @@ overwritten with zeros.  With
 the block where the superblock would be is overwritten even if it
 doesn't appear to be valid.
 
+.B Note:
+Be careful to call \-\-zero\-superblock with clustered raid, make sure
+array isn't used or assembled in other cluster node before execute it.
+
 .TP
 .B \-\-kill\-subarray=
 If the device is a container and the argument to \-\-kill\-subarray