+1 on esata. Definitely wouldn't go usb.
When I had to replace my Iomega SAN box, I just built up a cheap machine, that had raid on the mobo, and stuck 2 2TB drives in it, and mirrored them. It was actually slightly cheaper than buying a prebuilt SAN box.
That machine runs headless in my closet. When I need to get to it, I use remote access.