Hibernator: helping disk arrays sleep through the winter

Energy consumption has become an important issue in high-end data centers, and disk arrays are one of the largest energy consumers within them. Although several attempts have been made to improve disk array energy management, the existing solutions either provide little energy savings or significantly degrade performance for data center workloads.Our solution, Hibernator, is a disk array energy management system that provides improved energy savings while meeting performance goals. Hibernator combines a number of techniques to achieve this: the use of disks that can spin at different speeds, a coarse-grained approach for dynamically deciding which disks should spin at which speeds, efficient ways to migrate the right data to an appropriate-speed disk automatically, and automatic performance boosts if there is a risk that performance goals might not be met due to disk energy management.In this paper, we describe the Hibernator design, and present evaluations of it using both trace-driven simulations and a hybrid system comprised of a real database server (IBM DB2) and an emulated storage server with multi-speed disks. Our file-system and on-line transaction processing (OLTP) simulation results show that Hibernator can provide up to 65% energy savings while continuing to satisfy performance goals (6.5--26 times better than previous solutions). Our OLTP emulated system results show that Hibernator can save more energy (29%) than previous solutions, while still providing an OLTP transaction rate comparable to a RAID5 array with no energy management.