A fault-tolerant continuous media disk array under arbitrary-rate search

Multimedia data, especially continuous media including video and audio objects, represent a rich and natural stimulus for humans, but require a large amount of storage capacity and real-time processing. End user operations consist of arbitrary-rate search, pause, and others as well as normal-rate play. FF (fast-forward) and FB (fast-backward) among those operations are desirable to find out the scene of interest, but they require non-sequential accesses of disks. When data accesses are clustered to several disks without considering load balance, high quality services in playback may not be available. In this paper, we propose a new disk placement scheme, called PRR_gp (prime round robin with grouped parities), to enhance reliability using the wasted disk storage spaces, in which continuous media are placed on a disk array to distribute disk accesses uniformly. The PRR_gp can not only achieve load balance of disks consisting of a disk array under arbitrary-rate search like PRR (prime round robin), but also improve reliability by storing parity information on the redundant disk spaces appropriately. We use combinatorial and Markov models to evaluate the reliability of a disk array. The previous PRR scheme cannot tolerate more than two simultaneous faults. However, about 30% of the simultaneous faults can be recovered using our PRR_gp scheme