vol move 7-Mode is only for SAN data... snapmirror would be a quick cutover otherwise but a short downtime window. The 7-Mode root volume will need a takeover/giveback to move but that can be done quickly.
Are you running MultiStore or vFilers? They work great for this using data motion for vFilers or vFiler migrate to move the vFiler between controllers (and back or just leave them swapped) when swapping out back-end arrays.