Analysis of disk power management for data-center storage systems

Up to one third of the electricity supplied to a data center is required for the operation of the storage subsystem. A typical data-center workload, characterized by short idle periods, prevents traditional disk power management (DPM) from saving energy. This paper starts with an analysis of DPM's traditional timer-based disk spin-down policy. Next, we examine how a multispeed disk adapts DPM to data-center workloads. Finally, we determine how to shape the workload to enable DPM on conventional server disks. All analysis is based on an analytical model for the energy consumed by a disk during an idle period. In addition, we assume standby power to be non-negligible. The results are that (1) the competitive ratio of a threshold-based disk spin-down policy depends on the ratio of standby power to idle power, (2) the notion of break-even time can be generalized for multispeed disks, and (3) DPM saves most energy when mean idle time and idle-time variance are maximized. With this analysis, the authors intend to stimulate the design of new data-center file and storage systems that optimally exploit DPM to save energy