Adaptive Block Rearrangement Under UNIX

An adaptive UNIX disk device driver is described. To reduce seek times, the driver copies frequentlyreferenced blocks from their original locations to reserved space near the center of the disk. Block reference frequencies need not be known in advance. Instead, they are estimated by monitoring the stream of arriving requests. Measurements show that the adaptive driver reduces seek times and response times substantially. 1 Introduction Disk performance can be a limiting factor in the performance of a computer system. The problem of slow secondary storage devices has come to be known as the I/O bottleneck. One of the major components of disk access times is seek time, the time required to move the drive's read/write heads to the required data. By reducing seek time, the performance of a disk can be improved. In a recent paper [Akyurek 93] we introduced an adaptive block rearrangement technique which reduces disk seek times. Under this technique, a small number of frequently refere..