Real-time disk scheduling for the mixed workloads of multimedia data

Abstract

With fast advances in the computing power and networking technologies, demands for presentations of time-based data increasingly grow in the computing industry. Time-based data such as digitized video and sound are frequently called the continuous media since the playback of such data requires continuous data retrievals during the period of play-back. For the continuous media playbacks, disk-resident data should be read for the online delivery towards a client``s device so that the device continuously consumes data at a specific rate in order to reproduce a sequence of frames or sampled sounds. This requirement for the continuous media playback is referred to continuity requirement. Such continuity requirement should be fulfilled by a continuous media server that provides concurrent play-backs of continuous streams in online mode. To this end, the continuous media server is designed to have a deliberated algorithm for real-time disk scheduling meeting the continuity requirements of simultaneous continuous media streams. Besides the data requests from continuous media streams, there may exist data requests asking for time-independent data such as images, textual files, HTML documents stored in the continuous media server. Therefore, the continuous media server also needs to provide a mechanism to read time-independent data without missing deadlines of continuous requests. The mixed service of continuous requests and time-independent requests is a tough problem to be tackled in this dissertation. In this dissertation, we first develop a new scheduling method combining the EDF algorithm with the SCAN algorithm to service a number of continuous media streams. In the previous works, the combination of these two algorithms has been done such a limited way that the SCAN algorithm is applied for a small number of data requests with the same deadline. Since the SCAN algorithm cannot reverse the direction of disk head movement for a long while and retrieval orders of dat...