Implementation of Hibernator (Qingbo Zhu, et al 2005), "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. The goal of the Hibernator is to choose, at the start of each epoch, for each disk i, a speed j that minimizes the total predicted energy consumption subject to a constraint that the average response time be no greater than Rlimit"