Disk Striping and Block Replication Algorithms for Video File Servers

In multimedia systems, compressed video files are stored digitally on disks within a video server. Object placement and object replication on disks influence the cost, the availability, and the throughput of a video server. The choice of algorithm, along with the work-load, determines the number of disks needed to support a given number of users. There is a need to duplex video objects in order to provide reliable access in the event of disk failures. Duplexing also provides an opportunity to optimize I/O and improve throughput by providing two potential sources for each block. The Individual Permutation Algorithm uses a different permutation of disks for each movie. This paper studies the performance impact of different means of selecting permutations. The value of dynamic load balancing afforded by duplex is also studied. Part of the mtoivation of this study was to better understand the wide striping of the IBM Tiger Shark video server. Simulations show that the choice of algorithm leads to maximum practical device utilizations from 63 to 95 percent, resulting in significant differences in system cost.