Well, first the Visionsat takes a USB 2.0 hard drive.
That could be any ATA/IDE ...or... SATA drive in an external cabinet with at least a USB 2.0 interface.
I'm currently using a new Western Digital 500gb external USB drive.
Think it was $79 ? after rebate at one of the usual office stores.
Came with its own small switching power supply.
Previously, I'd used an external WD Portable drive
That's where they put an IDE laptop drive in a little box with USB interface, and power the whole thing through the USB cable.
Used a 60gb unit, and it worked dandy.
If I had to guess, I'd suspect it was 4200rpm, not 5400, nor the more common 7200 you see in real drives.

It would record one show, while playing another.