Quantum has 1tb of storage.
Verizon doesn't intend for DVR to be loing term storage.
Keep in mind that if you use an external drive and the most DVR dies, you lose everything on the external drive.
And quantum costs more not only because if extra storage. It has features that older models don't. Lime streaming DVR programs outside the home.
And I just saw a post on another forum that a total vod relaunch is coming to quantum only.