Just how often do hard drives fail? A lot more frequently than the manufacturers claim, according to a study
done by Carnegie Mellon University. The study, which compared the failure rates of many SCSI, FC and SATA drives, determined that the failure rate for most drivers was between 2% and 4%, and as high as 13% in some scenarios. This is in stark contrast to the manufacturers, who list a failure rate of around 0.88%.
Where does the discrepancy come from? The study itself has points of failure, such as factoring in drives that were RMA'ed though not necessarily failed. Of course, a simulated environment in which the manufacturer tests equipment won't compare to the real world, where millions of possibilities for damage to the drive exist. They are often dropped, put in poorly ventilated chassis, put in excessively humid environments and others. Still, the study is interesting – and worth a read.