It's important for people to realize that hard drives crash. I've been telling my friends for a few years to start thinking about getting their data on more than one external drive because their treasured external drives will eventually crash.
It's not uncommon for people in my line of work to have an external drive with quite a bit of reference data on it for use in their job. Sometimes they also keep personal documents accessible at work without having to put it on the company server. Seems like a good plan until it all goes horribly wrong.
This week I heard about a hard drive at work melting down as it was transferring data and the poor owner looking on as he lost everything. I'm glad I wasn't in the room. Imagine how that must have felt.
There is a phrase of speech in the military that goes something like "if you have one, you have none. If you have two, you have one." This is of course speaking of redundancy and the need to keep a second set of data, preferably at another location.
If you don't believe me, check out this annual update from Backblaze, they track the life of the hard drives they use to backup your data. I'm a Crashplan customer, but either is good. You'll also see they recommend the Western Digital over Seagate. You can say all of this is over the top, but at least you won't have to listen to me say "I told you so" when your disk crashes.
I just signed up for Backblaze...if I like it I intend to switch from Crashplan.