You have to either make sure no one is pushing backup/archives to the disks
or do the old
vary offline xxx
upd vol xxx acc=reado
vary online xxx
move data xxx stg=blahtape
upd vol xxx acc=readw  (you can do this while the move is running 'cause the
move data has it locked to writes)

Otherwise your inbound clients will blow off if you just do a move data...
the process will lock the disk and clients fail with no space available on
server (or something like that) but the above process does this all cleanly
(if you don't know about current client activity on the box)

Dwight