A distributed fault-tolerant design for multiple-server VOD systems

Fault tolerance is an important design criterion for reliable and robust vi deo-on-demand systems. Conventional fault-tolerant designs use either a pri mary backup or an active replication method to provide system fault toleran ce. However, these approaches suffer from low utilization of the backup or replication system. In this paper we propose two playback-recovery schemes for distributed video-on-demand systems called the forward playback-recover y scheme and the backward playback-recovery scheme. Unlike conventional fau lt-tolerant designs, our schemes use existing playback resources to recover faulty playbacks without allocating new resources, significantly reducing recovery overhead. To use the schemes effectively, we developed a distribut ed algorithm for determining the order and gap information between the play backs on the distributed video-on-demand servers so that overhead for recov ering from a server failure can be minimized. This algorithm achieves N - 1 fault-tolerant resiliency for N-server video-on-demand systems. In additio n, three server-recovery policies are also presented to guide surviving ser vers in applying the proper scheme to recover faulty playbacks, thus reduci ng overall recovery costs. Simulation results show that the proposed recove ry schemes are effective and useful in designing fault-tolerant multiple-se rver video-on-demand systems.