Multimedia systems store and retrieve large amounts of data which require extremely high disk bandwidth and their performance critically depends on the efficiency of disk storage. However, existing magnetic disks are designed for small amounts of data retrievals geared to traditional operations; with speed improvements mainly focused on how to reduce seek time and rotational latency. When the same mechanism is applied to multimedia systems, overheads in disk I/O can result in dramatic deterioration in system performance. In this paper, we present a mathematical model to evaluate the performance of constant-density recording disks, and use this model to analyze quantitatively the performance of multimedia data request streams. We show that high disk throughput may be achieved by suitably adjusting the relevant parameters. In addition to demonstrating quantitatively that constant-density recording disks perform significantly better than traditional disks for multimedia data storage, a novel disk-partitioning scheme which places data according to their bandwidths is presented.

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On the Internet, multimedia objects are stored in content servers. The clients behind some proxy servers are located over a wide area network (WAN) far from the content servers (Figure 1). When a client accesses multimedia objects from a content server, the content server must either allocate sufficient disk and network resources to multicast or unicast the objects to the client (Ma & Shin, 2002). Otherwise, it rejects the client. Thus, the popular content server becomes the bottleneck in delivering multimedia objects. Proxy servers have the disk cache space, network bandwidth, and availability to cache parts of the multimedia objects for clients, making them good candidates to solve the bottleneck problem. However, large multimedia objects are not cached or only partially cached in current proxy servers. When fast optical networks are widely deployed, this problem is becoming more severe. Therefore, proxy caches must be enhanced to alleviate the bottleneck in popular content servers with multimedia objects. Multimedia proxy servers perform several functions in accessing multimedia objects over the Internet. We first present the background in the next section. Next, the cache replacement policies being used in proxy servers are described. Then, the object partitioning methods are described. After that, the transcoding method that converts high-resolution objects into low-resolution objects is described. Afterward, we present the cooperative caching method that can be applied to cache objects on proxy servers. Lastly, we describe a method to distribute proxy-server load using a depot.