A number of people disagreed with my statement about all hard drives being approximately equal in reliability. I based that statement on my experience and on the fact that when I looked at the MTBF (Mean Time Between Failure) ratings for modern drives, all stood between 150,000 hours and 500,000 hours - 17 to 57 years of non-stop service between failures. People who had problems with drives in the past have a point, since MTBFs used to be around 10,000 hours, or just over a year of non-stop service. If the drive is a file server, 10,000 hours is not enough, but if you power on the machine for just a few hours each week, 10,000 hours should last quite some time. I'd like to know exactly how a manufacturer determines MTBF ratings - I know of no empirical test that condenses 57 years of non-stop service into a few months. That's not even taking into account additional wear from being turned on and off repeatedly and other environmental stresses.
A low MTBF could be balanced by a generous warranty period. Standard warranties range from ninety days to five years, and frankly, I'd recommend that you go for a longer one, at least two years. Five years is great, but if the drive dies in the fourth or fifth year, you may end up discarding it anyhow to buy a new one that's far larger or faster. Five years ago I used a home-assembled 30 MB Seagate 238R (5.25") hard drive in a case that sounded like an airplane and had room and power for four half-height drives. Now I use a 1.2 GB Quantum (3.5") that's far faster and more spacious. If I still had that 30 MB drive, I doubt I'd use it seriously even if its warranty was still good.
As an additional warning, David Stodolsky <email@example.com> writes:
The exact same drive model obtained from different sources may be of substantially different reliability. When Quantum sells drives to Apple, Quantum knows that the drives must pass rigid requirements and will be tested by Apple and sent back if they fail (perhaps with hefty penalties and cancellation of the delivery contract). The same drive from La Cie, wholly owned by Quantum, may be one that did not meet Apple's standard! (I got four bad drives in row from La Cie.) Even worse, Quantum has released new models under the same model number. In some cases, manufacturers have been known to swap parts among drives not up to spec to get a drive that then passes (barely). Ehman was found to be shipping used drives as new. This is outright fraud, but it can happen, as I found out with one of my drives.
Apple tests different drive models before approving models for its machines. Some aren't approved, and if you buy one of these drives you may have trouble, especially if you run A/UX or some high-end multi-media applications. Know your drive supplier and the specs on the mechanism if you want to avoid trouble. For the average user, a reliable supplier with good service in case a drive must be returned is of paramount importance.