OP...If you want a reliable external HD, try 2 or 3 little netbooks. I've found computer HD's are pretty reliable. Always remember...two is one and one is none.
I BU on 3 - 4 computers, 3 external HD's, 2 brands of DVD's (One brand is commercial, one brand is gold archival) and store some DVD's off site if a fire hits. One external HD is the desk model next to the computer. The other two HD's are different brands that are portable and go in a fire safe.
I also don't erase the mem cards I use. I got 6 bodies, each has a card and the cards take a long time to fill up. When they get near full, I pop in an empty card. So there is BU overlap here as well.
Now, I don't go BU crazy with all my stuff. The only things that go on the DVD's are my very good digital work and all my older good work that was scanned from negs. I don't want to lose my scanned negs. It will take years to get that work done, so BU overkill is cheap insurance for it.