Exploitation of disk cache for VOD services in network-attached storage systems

Modern storage systems become network-accessible. One of the leading network-attached storage systems is the Fiber Channel Arbitrated Loop (FC-AL). In order to further exploit the performance of the FC-AL-based video systems, we have built the end-to-end emulation by putting all system components together. The results showed that the system improved performance compared to conventional SCSI-based systems, but disk cache utilization among disks is similar but quite low. In this paper, in order to exploit the unused disk cache blocks, we employ prefetching. We describe how to determine FC-AL acquisition order and time among disks in advance. Then we propose a cache replacement policy to take full advantage of the sequential access pattern of video files and show how to estimate the maximum number of prefetched blocks. By analysis and simulations based on one-disk configuration, we show that the prefetching not only increases the total number of concurrent streams, but it also further utilizes the FC-AL.