hello.. is a 3tb external drive ok to use w/ the hr24-500? its for my parents. once the external drive is pluged into the dvr, do i just plug in the dvr and turn it on? and if the dvr only uses the external drive, if they want to watch anything on the old one, do they need to unplug the external drive then reboot, or turn it on? No way to transfer the old drives contents to external one? Thanks for your help guys..