What's the expected lifespan of a hard drive? All my backup data (photos, games, etc.) is on a 1TB external drive... so when should I back up my backup? Is there anything I can do to keep it safer? - Ron M.
The lifespan of any hard drive is about five minutes. Really, a backup drive can hold data for 8 years or even longer—hell, maybe decades if you almost never use it and keep it in a climate-controlled box—but it would be a mistake to assume that any one hard drive is in it for the long haul. Having multiple backups is always wise, so for irreplaceable data, I always assume that any drive could fail at any time: today, tomorrow, in five minutes from now.
But if you're just storing things for convenience—i.e. games you want on hand without having to redownload them—then depending on how much you use the drive, you can hope for five to eight years. I have an external SimpleTech [re]drive from 2008 or so that's plugging along fine, and since nothing on it is all that important, I haven't bothered to buy a new one. It may fail soon, or it may last another four years. Unfortunately, you can't really be sure.
A lot of variables can contribute to hard drive failure. A mechanical bit can fail, circuitry can fail, dust can get on the plate, the recording medium can just get old, temperature and humidity are a factor—it's not possible to accurately predict the lifespan of any one drive. When in regular use, you might have a failure in the first year, or after a solid six years. They'll all fail eventually.
For a couple years, online backup service Blackblaze has been publishing hard drive failure rates based on its large data center. In 2013, the site reported that 78% of its drives last longer than four years. That's not too bad, but it means that if you've been using your primary hard drive for five years, it might be time to look at a new one—or at least back up anything important.
More recently, Blackblaze found that 4TB drives seem to be especially reliable. "We like every one of the 4 TB drives we bought this year," it wrote. "For the price, you get a lot of storage, and the drive failure rates have been really low. The Seagate Desktop HDD.15 has had the best price, and we have a LOT of them. Over 12 thousand of them. The failure rate is a nice low 2.6% per year."
For backup drives, I think it's reasonable to expect quite a few operational years. But be aware that, whatever the statistics may be, hard drives fail. If it's about time to get a new backup drive, The Wirecutter (a site I trust greatly) recommends the 4 TB WD My Book. As for SSDs, our review of the OCZ Vector 180 goes into some detail on their lifespans.