[Raapys]

You need identical and clean drives to set up a raid array, from what I know. You also need a raid controller.

I've to agree with CW; backup drives are rather unncessary for home/personal use computers, unless you're storing very important documents. I've never once actually had a drive fail on me, this with 4 desktop PC's and 6 laptops over a period of 10-12'ish years.

The cheapest 500gb drives seems to be at around 100-125$, both internal and external, I believe. Don't have much experience with external drives myself though, so I'm unsure how reliable they are.