This might seem like a mundane question, but it’s actually pretty interesting because the answer is: “No one knows.” Backblaze is finding out, however. They are a cheap backup service (I use them) like the better-known Carbonite. They are famous, in addition to low prices, for building their own racks to stick hard drives in and then open-sourcing the designs so you can build your own, if you like. What’s more: they use standard, commercial disk drives. The same kind that you might have in your desktop. Which means, with a sample size of 25,000 drives, they’re a pretty good source if you want real-world numbers on how long these puppies last.
The whole article is really worth reading, but the take away is that–if current trends continue–the median life for a commercial disk drive is about 6 years.