Q You remark that modern hard disks often fail shortly after their warranty expires. I am about to buy a new iMac and MacBook Pro. What should I use as an archive if I cannot trust modern external hard drives?
A You can trust hard drives, but you need to know how far that trust can safely extend.
Good enterprise-quality hard disks – for which you will pay a premium – typically have five year warranties, and show low failure rates until they have passed out of warranty. Provided that you minimise stress on them, by spinning them up as infrequently as possible, and not subjecting them to excessive heat, high humidity, shocks or jolts, you can trust them for day-to-day data storage within that warranty period and often well beyond.
Valuable (including personally precious) files should also be archived to media that are even more likely to last robustly for a decade or more, and at the moment probably the best choices are high quality DVD-R disks that are then stored in cool and dark conditions. To add braces to that belt, you should also store copies of those optical disks off-site.
More capacious and accessible archives can be maintained by replacing your Time Machine backup disk when it becomes full, and storing full disks carefully, but they are not likely to prove as reliable over time as optical disks which have been properly stored.
Updated from the original, which was first published in MacUser volume 26 issue 24, 2010.