The four major factors that have driven the reduction of the cost of disk-based archiving are as follows:
- Increasing disk capacity (density) for a hard drive of a given price
- Transition from the use of enterprise disks to the use of consumer grade SATA disks
- Transition from storage interconnection via Fibre Channel to switched SAS and Ethernet
- Transition from customer storage controllers to commodity servers and software
As a consequence, the rapid decrease in the cost of disk-based archiving is not a result of the intrinsic reduction in the cost of disk storage, but rather is a reduction in the cost of the overall system. And now that this reduction in cost has already largely occurred, the rate of cost reduction flattens out to more closely approximate the reduction in the cost resulting from increasing disk density.
This is a critical point to understand when comparing the costs of disk archiving to tape archiving, since many cost projections have made the assumption that this rate of reduction of disk cost will continue into the future.