SDI Seminar

Mootaz's Abstract Speaker: Elmootazbellah Elnozahy, CMU

Storage Strategies for Video Servers

Date: Thursday, February 22, 1996

Abstract: A cluster-based video server acts as a parallel processor that provides the aggregate I/O and network bandwidths of the component machines. An accepted practice in such environments is to use RAID-like schemes that store error correcting code (ECC) in addition to the video data. Should a failure occur, the unavailable data can be computed on the fly using the ECC and the service continues at the same quality. In cluster-based systems, however, the video data are distributed over several servers and there is no convenient point to reconstruct the missing blocks except at the client. Relying on the client for this task is not desirable as it may not have the necessary buffering or processing capacity.

My argument is that a better alternative to RAID-like schemes is a strategy that exploits the inherent characteristics of the compressed video stream to tolerate partial failures. This talk presents two approaches for storing MPEG video that helps in tolerating partial failures in server clusters at the expense of marginal degradation in the quality of service. The first approach restricts ECC storage and computation to reference frames, ignoring low-information frames. The second approach uses the structure of the compressed video stream to substitute unavailable high-information frames with equivalent low-information frames.