Resumen
Hard-disk drive (HDD) reliability has always been a significant weak link, perhaps the weak link, in data storage. In the late 1980s people recognized that HDD reliability was inadequate for large data storage systems so redundancy was added at the system level with some brilliant software algorithms, and RAID (redundant array of independent disks) became a reality. RAID moved the reliability requirements from the HDD itself to the system of data disks. This article identifies significant HDD failure modes and mechanisms, their effects and causes, and relates them to system operation. Many failure mechanisms for new HDDs remain unchanged from the past, but the insidious undiscovered data corruptions (latent defects) that have plagued all HDD designs to one degree or another will continue to worsen in the near future as areal densities increase.