Performance issues in CD-ROM-based storage systems for multimedia

CD-ROMs have proliferated as a distribution media for desktop machines for a large variety of multimedia applications. We look at issues related to the single-user desktop environment. Since these multimedia applications are highly interactive in nature, we take a pragmatic approach, and have made a detailed study of the multimedia application behavior in terms of the I/O request patterns generated to the CD-ROM subsystem by tracing these patterns. We discuss prefetch buffer design and seek time characteristics in the context of the analysis of these traces. We show that it is best to place multimedia streams near the center of the CD-ROM. We present the parameters of an adaptive main-memory hosted cache that receives caching hints from the application to reduce the latency when the user moves from one node of the hypergraph to another. We show that short-throw seeks of distance 100 are the most important. We look at the use of CD-ROMs in a video on demand server (VoD) and discuss the problem of scheduling multiple request streams and buffer management in this scenario. We adapt C-SCAN (Circular SCAN) algorithm to suit the CD-ROM drive characteristics and prove that it is optimal in terms of buffer size management. We provide computationally inexpensive relations by which this algorithm can be implemented. We then propose a 'constant-full-load' admission control algorithm which admits new request streams from a pool of dummy requests without disrupting the continuity of playback of the previous request streams. The algorithm also supports operations such as fast forward and replay.