Exploiting redundancy to construct energy-efficient, high-performance RAIDs

Recent studies show that disk-based I/O subsystems account for a non-trivial portion of energy consumption in data-intensive environment such as storage servers and data centers. Previous powerefficient I/O solutions for a single disk drive or mobile computers cannot be applied to data-intensive environment where the I/O load is much more intensive. Current solutions seek help from multi-speed disks but this type of disk will not be on the market soon. Solutions have to be sought on extensions on conventional storage system techniques such as RAIDs. This paper seeks a novel way to build EnergyEfficient, high-performance RAID system called EERAID by exploiting inherent redundant information such as mirroring and parity at the RAID controller level. As representative mirroring and parity redundant RAID systems, RAID 1 and RAID 5 are particularly studied. For RAID 1, we develop a Windows Round Robin (WRR) request scheduling policy. For RAID 5, we introduce a Transformable Read policY(TRY) to transform disk requests from spun-down disks to active disks, and develop a Power and Redundant Aware Destage policy (PRAD) to defer writes to work together with TRY. Comprehensive trace-driven simulations show that EERAID can significantly conserve energy with a minor performance impairment, by 12-30% energy saving for both small-scale and large scale RAID level 1, and 10-20% energy saving for small-scale RAID level 5.