A number of techniques have been developed for maximizing disk utilization in media servers, including disk arm scheduling and data placement ones. Instead, in this paper we focus on how to efficiently utilize the available memory. We present techniques for best memory use under different disk policies, and derive precise formulas for computing memory use. We show that with proper memory use, maximizing disk utilization does not necessarily lead to optimal throughput. In addition, we study the impact of data placement policies including disk partitioning and multiple disks. Finally, our analysis shows that maximizing disk utilization and disk striping incur high system costs, and are not advisable in a media server.

Interactive multimedia applications require fast response time. Traditional disk scheduling schemes can incur high latencies, and caching data in memory to reduce latency is usually not feasible, especially if fast-scans need to be supported. In this study we propose a disk-based solution called BubbleUp. It significantly reduces the initial latency for new requests, as well as for fast-scan requests. The throughput of the scheme is comparable to that of traditional schemes, and it may even provide better throughput than mechanisms based on elevator disk scheduling. BubbleUp incurs a slight disk storage overhead, but we argue that through effective allocation, this cost can be minimized.

Conventional wisdom holds that reducing disk latency leads to higher disk utilization, maximizing disk utilization leads to higher throughput, and employing a faster disk leads to better performance. All of this is true when building a conventional file or database system. In this paper we show that these principles can be misleading when applied to a media server. To design such a server, we propose a cost-based approach that focuses on the perstream costs. We give various examples to illustrate the design process. Keywords: multimedia, disk latency, memory utilization, per-stream cost. 1 Introduction Maximizing throughput is a common design objective for a media server. To improve throughput, two approaches have been used: reducing disk latency (i.e., seek overhead and rotational delay) and minimizing the required memory. To reduce disk latency we can either employ efficient disk scheduling [13, 14, 15] or enact intelligent data placement policies [9, 11]. Both methods effectively ...

A number of techniques have been developed for reducing disk latency in a video server, including disk arm scheduling and data placement ones. In this paper we carefully study memory utilization in video servers, leading to enhanced techniques that significantly reduce memory use. This is achieved by introducing artificial delays between IOs. Surprisingly, the delays lead to better overall performance as compared to "traditional" disk latency reduction techniques. We also propose a novel disk scheduling policy that reduces initial latency (i.e., the time between the arrival of a request and the start of the presentation) to minimum. In addition, we study the memory requirements and costs of a video delivery system, showing how data placement on disk and multiple disks impact memory use. In doing so we show that it may not be advisable to achieve the maximum throughput that a disk can support.