Intra-disk Parallelism: An Idea Whose Time Has Come

Server storage systems use a large number of disks to achieve high performance, thereby consuming a significant amount of power. In this paper, we propose to significantly reduce the power consumed by such storage systems via intra-disk parallelism, wherein disk drives can exploit parallelism in the I/O request stream. Intra-disk parallelism can facilitate replacing a large disk array with a smaller one, using the minimum number of disk drives needed to satisfy the capacity requirements. We show that the design space of intra-disk parallelism is large and present a taxonomy to formulate specific implementations within this space. Using a set of commercial workloads, we perform a limit study to identify the key performance bottlenecks that arise when we replace a storage array that is tuned to provide high performance with a single high-capacity disk drive. We show that it is possible to match, and even surpass, the performance of a storage array for these workloads by using a single disk drive of sufficient capacity that exploits intra-disk parallelism, while significantly reducing the power consumed by the storage system. We evaluate the performance and power consumption of disk arrays composed of intra-disk parallel drives, and discuss engineering and cost issues related to the implementation and deployment of such disk drives.