Hard drives, quality

[Jared Smith]

I'm buying four identical drives for RAID 5. I'm hoping to buy IBM, but if 
someone has a better suggestion, I'm open by virtue of good evidence. 
What puzzles me is, a 20G drive is $92. An 80G drive is $106.
What's up with that? I need stability above all; is the 20G
a better buy for this reason? Can anyone please explain
why it's roughly the same to buy these two very different sizes?

20G
http://www.googlegear.com/jsp/ProductDetail.jsp?ProductCode=100414

80G
http://www.googlegear.com/jsp/ProductDetail.jsp?ProductCode=100418

-Jared