Minimizing Power Consumption in Video Servers by the Combined Use of Solid-State Disks and Multi-Speed Disks

Disks use a considerable portion of the total energy consumed by a video server. Solid-state disks (SSDs) can be used as a cache to reduce disk speeds, thereby decreasing the power consumed by disks. However, effective SSD bandwidth management is essential to cope with the high request rates for popular video files stored on SSDs. To address this problem, we propose a new SSD cache management scheme for a video server that uses multi-speed disks. First, we introduce a storage allocation scheme to examine how the presence of an SSD cache affects disk bandwidth consumption. We then propose an SSD bandwidth allocation algorithm to minimize energy consumption by allowing disks to run at lower speeds while achieving jitter-free disk speed transitions and by limiting the number of transitions to ensure disk reliability. Our experimental results demonstrate that our proposed bandwidth allocation algorithm achieves appreciable power savings under various workloads while limiting the number of disk speed changes.