I just purchased a Dell optiplex 3020 with 8gb ram and i5-4570. So now I'm on my way to being a blue Iris afficianado. What size wd purple should I get? Will 2tb be ok? I plan on either going motion sensing or continuous record on a couple cams for now. How long could I record on continuous with 2 2mp cams on a 2tb HDD?