On reducing energy management delays in disks

Enterprise computing systems consume a large amount of energy, the cost of which contributes significantly to the operating budget. Consequently, dynamic energy management techniques are prevalent. Unfortunately, dynamic energy management for disks impose delays associated with powering up the disks from a low-power state. Systems designers face a critical trade-off: saving energy reduces operating costs but may increase delays; conversely, reduced access latency makes the systems more responsive but may preclude energy management. In this paper, we propose a System-wide Alternative Retrieval of Data (SARD) scheme. SARD exploits the similarity in software deployment and configuration in enterprise computers to retrieve binaries transparently from other nodes, thus avoiding access delays when the local disk is in a low-power state. SARD uses a software-based approach to reduce spin-up delays while eliminating custom buffering, shared memory infrastructure, or the need for major changes in the operating system. SARD achieves over 71% reduction in delays on trace-driven simulations and in an actual implementation. This will encourage users to utilize energy management techniques more frequently. SARD also achieves an additional 5.1% average reduction in energy consumption for typical desktop applications compared to the widely-used timeout-based disk energy management.