Your hard drive may not be as reliable as manufacturers would like you to think. Recent studies by researchers at Carnegie Mellon and Google suggest that vendor Mean Time To Failure (MTTF) ratings for hard drives are a bit misleading.
The Carnegie Mellon study, conducted at several locations, found typical failure rates of 2 to 4 percent and a high of 13 percent, in contrast to the less than 1 percent you'd expect based on vendor MTTF ratings (see
chart or click on the thumbnail image below). Google's study pegged the annual failure rate at about 3 percent.
Hard-Drive Failures Surprisingly Frequent