Intra - Disk Parallelism

Power is a big problem in data centers and a significant fraction of this power is consumed by the storage system. Server storage systems use a large number of disks to achieve high performance, which increases their power consumption. In this thesis, we explore an architecture that can significantly reduce the power consumed by the storage system 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 present an historical retrospective of intra-disk parallelism and show how technology has changed over time creating new demand for efficient designs. We also 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 conduct a bottleneck analysis to identify the key performance bottlenecks that arise when a storage array that is tuned to provide high performance is replaced with a single high-capacity disk drive. These are the bottlenecks that intra-disk parallelism would need to alleviate. We then explore a particular intra-disk parallelism approach, where a disk is equipped with multiple arm assemblies that can be independently controlled, and evaluate three disk drive designs that embody this form of parallelism. 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 compared to the multi-disk configuration. We then evaluate the performance and power consumption of disk arrays composed of intra-disk parallel drives and compare it with conventional multi-disk configurations. Intra-disk parallelism reduces the power consumed at the disk drives by