The Research Of Efficient Real-Time Disk-Scheduling With Fair Bandwidth Distribution

A multimedia server requires a real-time disk-scheduling algorithm to deliver continual multimedia streams which have the soft real-time requirement. Traditional disk-scheduling algorithms SCAN must be improved because it can not satisfy the real-time requirement of multimedia server.In this thesis a novel real-time disk-scheduling algorithm is proposed called SCAN-FBD (SCAN with Fair Bandwidth Distribution) to provide quality guarantees for all in-service streams encoded at variable bit rates and bounded response times for aperiodic jobs. SCAN-FBD divides a real-time stream into guaranteed jobs and optional jobs. The admission control admits a stream as long as its guaranteed jobs are satisfied. Its admission control and bandwidth revervation mechanisms provide quality guarantes for all in-service multimedia streams. For non-real-time requests, the algorithm provides reasonable response time through the reversed bandwidth. Workload monitoring and dynamic bandwidth assignment adaptively adjust the percentage distribution of disk bandwidth between real-time and non-real-time requests making reanonable use of disk bandwidth and further improve the throughput of disk. SCAN-FBD incorporates an aggressive policy to dynamically reclaim unused bandwidth during runtime. The reclaimed bandwidth is used to serve optional jobs or more aperiodic jobs.The performance of the SCAN-FBD algorithm proposed in the thesis is evaluated through a set of simulations. The experimental results show that SCAN-FDB provides significantly better quality for real-time streams and yields considerably shorter response times for aperiodic jobs. SCAN-FBD is an efficient and flexible algorithm.