Research Of Technology For Data Migration And Storage In The Parallel VOD System

With the rapid development of Internet and multimedia technologies, multimedia applications over Internet walk into people's lives gradually. As an important aspect of multimedia, video application over Internet is faced with new opportunity and challenge. A lot of users require high quality service, and the server needs higher performance and efficiency. All these bring new technical issues into video applications. Bandwidth of networks and performance of video server are two main factors that restrict the utility of video applications. The video server with parallel architecture can extend the area of video service system, because it can disperse users' requests and reduce the local load of server and local traffic of networks. There are three kinds architecture in the current parallel video server, such as clustered, distributed and parallel.In the environment of clustered video server, the advantage of adopting hierarchical storage architecture is its ability to assign the appropriate storage hierarchy to each program based on its locality of access. We propose two replacement algorithm of disk cache in the hierarchical storage systems to put the really popular programs into the disk cache. The algorithm use access frequency information as well as time information, which suit for large, scale VOD environment. The Algorithm adopts periodic stepwise updating to replace outdated information and can predict the change of access probability, so hot and forthcoming hot programs will be replaced to disk cache to improve the hit rate of cache. In addition, we propose a scheduling algorithm, which pre-fetch the program while system is idle in order to improve the performance of video server.The scalability and availability of system always are our attention in distributed video servers. This dissertation describes an autonomous distributed architecture of video servers, and it is constructed gradually. After discussing the strategies of data migration and scalability, we propose a dynamic data migrating algorithm comparing with disk cache in the clustered system.In the hierarchical parallel VOD system, video program are always striped across disks/nodes to acquire high availability of disk. In the clustered system, the data nodes have strong independency. In order to improve the concurrency, we put forward a sort of Redundant Array Of Independent Data Node (RAIDN), which is similar to RAID 5. We also discuss its fault tolerant and propose a parity extension algorithm called sequence-extend.At last, this paper proposes an application example of clustered parallel VOD systems and comes to a conclusion to the research. In the end, we make an expectation.