Adaptive block rearrangement algorithms for video-on-demand server

Video-on-demand (VOD) is increasingly becoming one of the most important and successful services due to the recent advances in storage subsystems, compression technology and, networking. Therefore, the investigation of various alternatives to improve the performance of VOD servers has become a major research focus. The reduction of disk access time through intelligent data placement strategies is one such avenue and is the theme of this paper: Movie rental patterns indicate that accesses to movies are highly localized with only a small number of movies receiving most of the accesses. In this paper we exploit the access patterns and propose an adaptive rearrangement of the blocks on each disk within the server. With this approach, the blocks of the movies with comparable access frequencies are kept closer to each other We analyze two rearrangement schemes, called centered and sequential. In the centered layout, blocks are placed according to their access patterns starting with the most popular movie at the center. The sequential layout places movies in the order of their popularity starting at the edge of the disk. We compare and evaluate, through an intensive simulation study, the effectiveness of these layouts with respect to arbitrary layouts. The simulation results indicate that significant disk improvements could be attained by adopting the proposed schemes, and that the centered layout is the best performer.