Semantic data placement for power management in archival storage

Power is the greatest lifetime cost in an archival system, and, as decreasing costs make disks more attractive than tapes, spinning disks account for the majority of power drawn. To reduce this cost, we propose reducing the number of times disks have to spin up by grouping together files such that a typical spin-up handles several file accesses. For a typical system, we show that if only 30% of total accesses occur while disks are still spinning, we can conserve 12% of the power cost. We classify files according to directory structure and see access hit rates of up to 66% for a power savings of up to 52% of the power cost of spinning up for every read in easily-separable workloads.