Segmented information dispersal (SID) for fault-tolerant video servers
Ariel C. Cohen, Walter A. Burkhard · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
Standard disk array fault-tolerance solutions such as RAID 3 and RAID 5 are unattractive for video retrieval workloads. RAID 3 organizations have dedicated parity disks which are not utilized during fault-free operation. When used for video workloads, RAID 3 also suffers from decreased performance due to the effects of its fine-grained striping. RAID 5 organizations perform well under fault-free conditions, but their performance under failure is poor: the load on the surviving disks in an affected parity group doubles; these disks become a bottleneck which may result in a loss of as many as half of the streams. We describe a data organization which performs as well as RAID 5 under fault-free conditions, while performing much better than RAID 5 under failure. Improved performance under failure is achieved by distributing the reconstruction load better. Our new approach offers certain advantages when compared to existing approaches which are based on balanced incomplete block designs (BIBDs): contiguity is maintained under reconstruction; a distinction is made between the reconstruction of real- time video data and less critical check data; a relaxed balance requirement results in solutions which are not feasible with BIBDs.