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The paper presents a performance evaluation method to design the disk subsystem of a Web proxy server. The subsystem has multiple disks on a shared I/O bus. The main feature of this method consists of two basic techniques. One is a parameter estimation method with well-organized measurement procedures on a minimum sized disk subsystem containing one disk attached to one I/O bus. The other is a system performance prediction method based on BCMP queueing network theory. We examine the performance of a target disk subsystem when several parameters (e.g., the disk I/O sizes and the number of disks and I/O requests, etc.) change. For calculating performance metrics with the BCMP queueing network model, we have modified the convolution method to reduce the number of convolutions from the number of connected disks to one. Using the convolution method, the throughputs are calculated for a target disk subsystem with the parameter combinations and are compared to the measurement ones. The comparison shows that prediction errors are between 10% and 20%, which is relatively good precision for an analytical performance model. The effectiveness of the performance evaluation method is examined by designing and developing a Web proxy server.