Time-aware prefetching for on-demand video services in a residential service gateway

摘要

With the recent advances in network technology, the number of high-speed networked homes increases rapidly and the enhanced services such as on-demand video services become feasible in terms of market maturity. Another trend is that storage systems become network-accessible. One of the leading network-attached storage systems is the Fiber Channel Arbitrated Loop (FC-AL). As a residential service gateway, the FC-AL-based servers can stably provide high quality video (e.g., DVD quality MPEG-2 stream) with thousands of clients between external service providers and local clients. In addition, in densely populated areas such as New York City, they can be much more cost efficient. Using our end-to-end simulation experiments to combine all the components, we have observed that FC-AL-based streaming servers perform better than SCSI-based systems, but there is still room for performance improvement. We are motivated by the fact that, unlike in SCSI-based systems, all the disks in FC-AL-based severs utilize only a small portion of their caches to a similar degree due to FC-AL fairness arbitration algorithm. Thus, we propose an effective prefetching scheme to improve the performance by further utilizing the disk cache. We show how the proposed scheme can determine the maximum number of prefetched blocks depending on the disk block and cache size. It is also shown how to find the optimal number of blocks transmitted to the FC-AL from the disk cache per FC-AL arbitration. In addition, we describe the cache replacement policy to take full advantage of the sequential access pattern of video files, and explain how to support multiple loops. By analysis and simulation experiments, we show that our prefetching scheme is not able to only increase the total number of concurrent streams significantly by reducing the disk seek time, but it can also further utilize the FC-AL by reducing the overhead of arbitration.