A survey of approaches to fault tolerant design of VOD servers: Techniques, analysis and comparison

Recent technological advances in digital signal processing, data compression techniques and high speed computer networking have made on-demand multimedia servers feasible. A challenging task in multimedia systems is to service multiple clients simultaneously, while satisfying the real-time requirement for continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a multimedia server can require a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Further, due to the real-time constraints, the reliability and availability requirements of multimedia systems can be more stringent than those of traditional information systems. In this paper we focus on the main tradeoffs and issues associated with providing fault tolerance in multidisk VOD systems. We illustrate these tradeoffs through a discussion of several fault tolerance schemes and present a framework for a performability evaluation of possible design choices. (C) 1998 Elsevier Science B.V.