Video on Demand Servers: Storage Architecture with Disk Arrays

Abstract

The storage organisation of Video on Demand (VOD) servers is an important issue in the design of VOD systems. VOD servers are responsible for storing videos in disks and feeding them to users on request. The strategy used for storing movies in multiple disks affects the overall server performance, especially when a large number of concurrent streams are supported. The existing phase based striping method used in VOD server tends to lead to areas of unutilised disk. This spare area becomes more significant as the number of disks in the server becomes large. In this paper we propose the Spare Phase Based Striping Method to utilise the spare area and further reduce the waiting time. In this method, we group together the spare disk space of each individual disk into one large single spare area and use it to duplicate the most popular movies. We also present the Half Reverse Phase Based Method for use as a data layout in the spare area. This method guarantees a maximum waiting time for popular movies, reducing RAM dependency in comparison with the Replication Scheme and improving the average waiting time. We evaluate our scheme by carrying out a simulation study to compare it with other schemes, particularly with regard to the usage of RAM and the average waiting time.