Dynamic Replication of Content in the Hammerhead Multimedia Server

In a clustered multimedia server, by periodically evaluating client demand for each file and performing selective replication of those files with the highest demand, the files can be distributed among server nodes to achieve load balancing. This technique is referred to as dynamic replication. Several dynamic replication policies have been proposed in the past, but to our knowledge, our work is the first to describe in detail the implementation of dynamic replication in a server cluster environment. In this paper, we describe the architecture of the HammerHead multimedia server cluster. HammerHead has been developed as a cluster-aware layer that can exist on top of existing commodity multimedia servers – our prototype takes the form of a plug-in for the multimedia server in Microsoft Windows Server 2003TM. Replicated state information is maintained using the Ensemble group communication toolkit. We briefly describe our own dynamic replication policy, Dynamic RePacking, and its implementation in the HammerHead server. Finally, we present early performance results from a prototype version of the HammerHead server.