Ah, my current RAW hard drive is just about full, so I'll go out today and get a new one. I thought I'd take a minute to talk about these little monsters while I was thinking about them.
I'd like to begin by thanking the manufacturers for selling them cheaper. About a year ago, I was paying 25 cents/GB for them on sale. Today, the one I'm looking at will be 12 cents/GB. Thanks!
I currently have 14 external hard drives. My workflow goes like this:
Download to HD RAW 1
Backup images to HD RAW 2
Process images from RAW and transfer them to HD PROC 1
Every night HD PROC 1 gets automatically backed up to HD PROC 2
So, I have four hard drives for current work. I used to backup everything on DVD, but with the file sizes of the images getting bigger, I now only backup processed jpegs to DVD. I can easily shoot between 10 and 20 GB of RAW photos in a single session, and backing these up with DVDs is a pain.
I've only had one external HD fail. For those of you who care, it was a Western Digital. It had lots of important stuff that I think was backed up, but I used to put the CDs on a spindle for storage, and it's such a pain to go back through the spindles, that I just let all that go (for now). Backing up to HD is much better because your work is organized and easy to access.