Measuring file access patterns in UNIX

UNIX is a disk-based operating system, where only the system kernel is always memory-resident. A combination of small block size, limited read-ahead and numerous seeks can severely limit the file system throughput. This paper presents a tool to study the file access patterns. Information derived from the data collected can be used to determine the optimal disk block size and also to improve the block placement strategy. The tool is a software monitor, installed at the device driver level, and triggered by every physical request to the disk handler. The design approach used to measure the average number of logical records accessed sequentially is described. An evaluation of the tool is also presented.