High availability in clustered multimedia servers

Clustered multimedia servers, consisting of interconnected nodes and disks, have been proposed for large-scale servers that are capable of supporting multiple concurrent streams which access the video objects stored in the server. As the number of disks and nodes in the cluster increases, so does the probability of a failure. With data striped across all disks in a cluster, the failure of a single disk or node results in the disruption of many or all streams in the system. Guaranteeing high availability in such a cluster becomes a primary requirement to ensure continuous service. In this paper, we study mirroring and software RAID schemes with different placement strategies that guarantee high availability in the event of disk and node failures while satisfying the real-time requirements of the streams. We examine various declustering techniques for spreading the redundant information across disks and nodes and show that random declustering has good real-time performance. Finally, we compare the overall cost per stream for different system configurations. We derive the parameter space where mirroring and software RAID apply, and determine optimal parity group sizes