Disk Scheduling with Dynamic Request Priorities

High performance servers in client/server distributed systems must manage and multiplex disk I/O resources eeciently and fairly between multiple clients. In digital multimedia systems, clients may make requests of varying urgencies. The traditional approach to this problem thus assigns priorities to disk requests. High priority requests are scheduled rst, with low priority requests served only when the high priority queue is empty. While this approach permits priority optimization, it ignores seek optimization. When the length of the high priority queue is short compared to the low priority queue, disk utilization is very low. In this paper, we present a priority inversion disk scheduling algorithm where both priority and seek optimization are considered. The algorithm is evaluated through detailed simulation and its performance is compared with traditional scheduling algorithms. We then identiied the conditions when our algorithm performs better. The simulation results show that under these conditions, we achieve close to 50% reduction in total system response time. Based on this, an adaptive disk scheduling algorithm was constructed which consistenly outperforms the traditional approach.