I use the following set-up:
- Extra hard disk for my PC - used for a back-up of my data only
- External raid drive - a Lacie 2big.
- A NAS drive - a WD My Book.
Backing up is automated using software, so I don't do anything manually. Back-up software has options to either back up specific folders whenever their content changes or at specific times. I use the former for most stuff.
I find it annoying that new computers contain a single massive drive - I'd rather have two smaller ones! There's no point in backing up to a different folder on the same drive - that's no help if the drive fails! It's easy installing a new internal drive in a desktop PC. Or use an external drive.
The raid drive is actually 2 drives but the PC sees it as one. If one drive fails, simply stick in a new one, and the raid drive will rebuild the "lost" content. Lacie drives are expensive but their are cheaper options that are just as good.
The above drives should all use a fast data connection. I use eSATA.
Finally, the NAS (network attached storage) drive. This doesn't attach to your PC but is instead plugged into your broadband modem. It's essentially your own personal cloud, like Dropbox. So, your PC sees this as a network drive. The WD My Books are very reliable and cheap, and is hidden in a cupboard.
As my data is backed up in essentially five places (the original, the extra internal drive, the Raid (counts as 2!), the NAS drive). I don't worry about disk failure - if one back-up dies, I'll replace it. All 5 drives aren't going to fail simultaneously! I can't believe a thief would bother looking for my Raid and NAS drives hidden away, and I guess my house could burn down - but there's such a thing as being too paranoid!
Anyway, the final back-up is that I have prints of my good photos in my studio, which is not in my house!