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Asynchronous/Multithreaded I/O on Commodity Systems with Multiple Disks - a performance study

The purpose of this dissertation is to test the hypothesis that an asynchronous/multithreaded I/O service can be used to exploit the potential for parallelism of commodity systems with access to multiple disks. Three working systems are contributed: a simulation of asynchronous I/O; a POSIX-compliant asynchronous I/O library; and an extensible C++ class library for comparative tests of I/O services. The results of a simulation study and tests on real systems are used to demonstrate that, under specified circumstances, a significant increase in average application throughput is achieved through the use of asynchronous I/O. The types of workload most likely to benefit from this performance gain are characterised. However, for multithreaded implementations of asynchronous I/O, the improvements are shown to be achieved at the expense of average response times. These costs, sometimes as much as an order of magnitude increase in response time, are quantified.