Abstract
We propose a novel double-layered disk array and a specially adapted skip search method for video servers using cyclic time slots for read control, and determine the following from a theoretical analysis of worst-case performance: The worst-case time-slot duration when using the latest banded-recording magnetic disk devices can be approximated by two aspects of the disk performance—the maximum access time and the average data transfer rate. The maximum number of read channels obtainable with conventional disk arrays exceeds that of conventional single-disk recording by a factor that has a limiting value of 1 plus the normalized maximum latency, which is approximately 0.7–1.1 times the actual latency in seconds. The new disk array can further improve this to a factor of 1 plus the permitted truncation time at the start of a video sequence, normalized to the maximum latency. In a reliable double-layered disk array, to which parity disks are added, the number of parallel disks per sub-array has an optimum value of several disks if there is no constraint on the truncation time. Furthermore, we investigate the functioning of the proposed array with an experimental video server, which can provide a hundred read channels of 1.5 Mbps video with a quick response time (a maximum latency of 1 second), and a permitted truncation time of 3 seconds. © 1997 Scripta Technica, Inc. Syst Comp Jpn, 28(3): 1–12, 1997
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