Design of fault-tolerant large-scale VOD servers: With emphasis on high-performance and low-cost

Recent technological advances in digital signal processing, data compressio n techniques, and high-speed communication networks have made Video-on-Dema nd (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these task s and realize economies of scale associated with servicing a large user pop ulation, a VOD server requires a large disk subsystem. Although a single di sk is fairly reliable, a large disk farm can have an unacceptably high prob ability of disk failure. Furthermore, due to real-time constraints, the rel iability requirements of VOD systems are even more stringent than those of traditional information systems. Traditional RAID solutions are inadequate due to poor resource usage. Thus, in this paper, we present alternative sch emes which provide a high degree of reliability at low disk storage, bandwi dth, and memory costs for on-demand multimedia servers. Moreover, we discus s some of the main issues and trade-offs associated with providing fault to lerance in multidisk VOD systems. We would like to impress upon the reader that one of the main points of this paper is the exposition of trade-offs a nd issues associated with designing fault-tolerant VOD servers. It is not t he case that one fault tolerance scheme is absolutely better than another, but rather that one must understand the trade-offs as well as one's system constraints and then choose a fault tolerance scheme accordingly.