Effect of disk scheduling schemes on a video server for supporting quality MPEG video accesses

The difficulty of providing Video On Demand (VOD) with a guaranteed quality of service is primarily due to the variation in access latencies over the delivery path, from storage subsystem to network subsystem. In addition, with the bit rate variation inherited from MPEG encoding scheme, this problem becomes more severe. Because of the variation over the video delivery path and the degree of aggressiveness in an admission decision, the possibility of a system over-loading situation is highly likely. How this affects the service quality (especially jitter behavior) under different disk scheduling schemes used in VOD servers is not well known. In this paper, we intend to answer this question by conducting a simulation study of four basic disk scheduling schemes (First Come First Serve, SCAN, Circular SCAN and Earliest Deadline First). The result shows that each disk scheduling scheme demonstrates different behavior regarding to the number of supportable jitter-free streams, the number of jitter incidents, the number of streams affected by jitter incidents, the jitter frequency, and the jitter delay time. The implication to admission control strategy is discussed.