Trading disk capacity for performance

Improvements in disk access time have lagged behind improvements in microprocessor and main memory speeds. This disparity has made the storage subsystem a major bottleneck for many applications. Disk arrays that can service multiple disk requests simultaneously are being used to satisfy increasing throughput requirements. Higher throughput rates can be achieved by increasing the number of disks in an array. This increases the number of actuators that are available to service separate requests. It also spreads the data among more disk drives, reducing the seek time as the number of cylinders utilized on each disk drive decreases. The result is an increase in throughput that exceeds the increase in the number of disks. This suggests a tradeoff between the space utilization of disks in an array and the throughput of the array