Design and implementation of scalable continuous media servers

摘要

During the past decade, the information technology has evolved to store and retrieve continu- ous media data types, e.g., audio and video clips. Unlike the traditional data types (e.g., text), continuous media consists of a sequence of quanta, either audio samples or video frames, that convey meaning when presented at a pre-specified rate. A challenging task when implementing these servers is to guarantee retrieval and delivery of a clip at its pre--specified rate. Continuous media servers are expected to play a major role in many application domains including library information systems, entertainment technology. educational applications, etc. The focus of this study is on the disk subsystem of a server and techniques that both enhance its performance and ensure its scalability. By scalable, we mean that the system can grow incrementally as the requirements of an application grows in order to avoid a degradation in performance. This study details data placement techniques across both (1 ) the zones of a disk in order to trade bandwidth for storage, and (2) multiple disks to enable the system to scale. In addition, we describe scheduling techniques to (1) trade memory for disk bandwidth and vice versa, and (2) merge multiple requests referencing a single clip in order to increase the number of simultaneous displays supported by the system. We present performance results from Mitra, an experimental prototype that realizes an implementation of the presented techniques. These results demonstrate the feasibility of a scalable server.