In contrast to pure video servers, advanced applications such as digital libraries or teleteaching exhibit a mixed workload with massive access to conventional, "discrete" data such as text documents, images and indexes as well as requests for "continuous data". In addition to the service quality guarantees for continuous data requests, quality-conscious applications require that the response time of the discrete data requests stay below some user-tolerance threshold. We study the impact of different disk scheduling policies on the service quality for both continuous and discrete data. We identify a number of critical issues, present a framework for describing the various policies in terms of few parameters and finally provide experimental results, based on a detailed simulation testbed, that compare different scheduling policies.
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