In today’s world of large capacity disk drives, the probability that secondary device failures will occur has increased dramatically. Areal density, the amount of written information on the disk’s surface in bits per square inch, continues to outstrip Moore’s law. However, the reliability and performance of disk drives are not increasing at the same pace, and this is compounded by the growing amount of time it takes to rebuild drives.
Large capacity disks such as 16 TB and 20 TB SATA drives require much longer drive reconstruction times because each subsequent generation of disk still has the same number of heads and actuators servicing increased density platters. This significantly raises the probability of a multiple drive failure scenario.