Back your data up! That concludes lesson number one.
An external hard drive can be a lifesaver; as I discovered a few years back when my laptop hard drive went to heaven (actually, hopefully it went to hell, since it died on me at an inconvenient time). I lost several personal files.
With that out of the way, why just use one?
When it came down to protecting my data, especially gigs of data that take a long time to secure, I recognized that a backup drive can be just as prone to fail as any other. That’s why a raid solution works so well.
I went with a dual drive external Western Digital MyBook (pictured below). Looks the same as a standard external drive, just somewhat fatter. No hurt feelings, for it’s what’s on the inside that counts (at least in this situation), and that would be two accessible SATA 3.5” hard drives. These drives can be configured to be mirrored, striped, or treated as independent volumes. If you decide to go the mirror route, as I did, the device formats both internal drives as identical twins, and your computer simply sees them as a single external volume. If one drive dies, you’re safe; just pop the lid, remove the bad drive, play some taps, and put in a new one. The device will automatically mirror the contents for you. Both drives need to be of the same size and specs, of course.
Another perk is that it came with WD green drives, designed for low power consumption. It only uses power when reading or writing; otherwise, it stays in a powered down, suspended state. A slick feature, especially for a backup drive.
Ports on the model include Firewire 400, 800, USB 2.0, and ESATA.
Another closely related product is a media streaming / network version with a gigabit ethernet port. Same package, just designed to be attached to a home network rather then a computer. Not only does it serve as network storage, it includes media streaming capabilities, so iTunes and DLNA certified devices (like newer game consoles) can see and play media contained on it. It thus works nicely as a container for digital media as well.