Disk-based video-on-demand storage servers: requirements, challenges and (some) solutions

A video-on-demand (VOD) storage server is a parallel, storage-centric system used for playing a large number of relatively slow streams of compressed digitized video and audio concurrently. Data is read from disks in relatively large chunks, and is then "streamed" out onto a distribution network. The primary design goal is to maximize the ratio of the number of concurrent streams to system cost while guaranteeing glitch-free operation. This paper characterizes the VOD applications and then identifies several important issues along with an outline of possible approaches to dealing with them. Issues include the accommodation of unlimited demand for concurrent "private" viewing of the few hottest movies with limited resources, multi-zone recording and the resulting variable disk transfer rate, as well the interplay between fault-tolerance, load balancing, the size of RAM buffers and the organization of the storage subsystem.