Leahs Mom, I have the Seagate Backup Plus 2TB Slim External USB Drive. I have my main drive backed up on it, so no worries there. The drive that failed was for storage. Dh looked to see if it was still under warranty. They are under warranty for 3 years. This one is 3 years 4 months old, so out of warranty. It's a Seagate Barracuda, so not an off brand, or the cheapest on the market. I did expect it to last at least 4 years. Usually I begin changing them out when the get to be 4 to 4 1/2 years old.
Once in awhile, when we fix a computer for a friend, or something, the first thing we do is either back up their drive, or at least save the pics, music, and documents. We use one of the old hard drives for this purpose. At least 1 of them is 10 years old, and works fine. Another one is at least 8 years old, and it too is working great. While I don't expect them all to last that long, like I said, I did expect it to go at least 4 years.