Optimizing Prefetch in a Residential Gateway with Networked Storage Systems

VOD services require the storage system support with multiple disks. SCSI-based systems are usual choices. However, disks can be attached directly to networks these days. Fiber channel arbitrated loop (FC-AL) is a leading network-accessible storage interface. As a residential service gateway, the FC-AL-based servers enable the stable delivery of high quality video to thousands of clients between external service providers and local clients. We have observed that, even though they performs better than conventional SCSI-based systems, all the disks in FC-AL-based VOD servers utilize only a small portion of their caches to a similar degree due to FC-AL fairness arbitration algorithm. In this paper, we analyze the impact of prefetching on the performance of the FC-AL-based systems according to disk block/cache size. Analysis is also focused on how to find the optimal number of blocks transmitted to the FC-AL from the disk cache per FC-AL arbitration among multiple disks. Finally, simulation results show that a 16-disk system provides over 800 concurrent video streams with quality guarantee, supporting our analytical model