Can gnucmp be run on raw devices to compare filesystems?

[Amanda Wolbrum]

I apologize in advance is this is the wrong help list for cmp.  If it 
is, if someone could point me in the proper direction, that would be a 
big help.  Please cc me in any responses to the query as I am not 
subscribed to this alias.  Thanks!
I was wondering if cmp or gnucmp can be run on two raw devices to find 
out if there are differences between the filesystems.  Specifically, I 
have broken an existing mirror on my system and created two separate 
volumes around each plex.  Then, I am running the gnucmp command to see 
if the two filesystems/volumes differ.  Does anyone know if this using 
gnucmp in this way can be expected to produce reliable results?
Here is the command syntax:

gnucmp -l /dev/vx/rdsk/testdg/testvol1 /dev/vx/rdsk/testdg/testvol2

For those who don't know volume manager, this is the same as running:
gnucmp -l /dev/rdsk/fs1 /dev/rdsk/fs2

Thanks so much!

Amanda Wolbrum