Saving energy in video servers by the use of multispeed disks

Energy consumption is an important issue in data centers, and disks use a significant proportion of the total energy. A promising approach to reducing disk energy consumption is to use multispeed disks with lower rotational speeds, and allowing disks to run slowly when workloads are light can reduce their large contribution to the power used by video servers. We formulate the prerequisites for speed reductions, and derive an energy model constrained by retrieval period. We then analyze the relationship between retrieval period, buffer size, and disk speed, and examine the effect of buffer allocation on energy consumption. We then propose a new video data retrieval scheme in which the retrieval period and the speed of each disk is dynamically changed to adjust disk bandwidth utilization, with the aim of allowing disks to run at lower speeds while guaranteeing jitter-free speed transitions. Experimental results show that our scheme achieves appreciable energy savings under all workloads. They also reveal that increasing the number of available speeds reduces energy consumption but the benefits gradually tail off.