backup-with-filesystem-snapshots: clarify archive

Clarify the wording of the "Archive a Snapshot" section.  A user encountered some confusion today around this.

Signed-off-by: Sam Kleinman <samk@10gen.com>

Author: devkev

source/tutorial/backup-with-filesystem-snapshots.txt

@@ -169,10 +169,10 @@ that you archive these snapshots and store them elsewhere.
 Archive a Snapshot
 ~~~~~~~~~~~~~~~~~~
 
-After creating a snapshot, mount the snapshot and move the data to
+After creating a snapshot, mount the snapshot and copy the data to
 separate storage. Your system might try to compress the backup images as
-you move the offline. The following procedure fully
-archives the data from the snapshot:
+you move the offline. Alternatively, take a block level copy of the
+snapshot image, such as with the following procedure:
 
 .. code-block:: sh
 
@@ -181,7 +181,9 @@ archives the data from the snapshot:
 
 The above command sequence does the following:
 
-- Ensures that the ``/dev/vg0/mdb-snap01`` device is not mounted.
+- Ensures that the ``/dev/vg0/mdb-snap01`` device is not mounted.  Never
+  take a block level copy of a filesystem or filesystem snapshot that is
+  mounted.
 
 - Performs a block level copy of the entire snapshot image using the ``dd``
   command and compresses the result in a gzipped file in the