I m getting a new MacBook and getting rid of an old iMac. I currently have movies/photos/music (called Media) on an external hard drive that bypasses my iMac. I will get a new external HD for time machine for the laptop. How do I set it up so that when I connect both my Mediaexternal HD and my Time Machine external hard drive, that the TM ext HD backs up my laptop and the Media HD? Thx.