In order to evaluate the computer system, we use mainly five methods; BMT, specific application program, performance evaluation tool, experimental approach, and the comparison of system specification. In case of large scaled system in real environment, I/O is very important to system performance and system environment is changed at any time or demand and need system performance tuning continuously. For the performance evaluation of large scaled system, we should have to focus on the change of the system environment like a system configuration, user, and program in real environment. In this paper, I propose a pgage concept of detecting the change of the system workload or the workload of I/O system call easily. Pgage is a counter of evaluating the ability of multiplexing of I/O and detect I/O-intensive job on the computer system by periodically. Pgage is called by snapshut function per specific time. In this paper, I set up the environment of BASE and TARGET system (MIX2, PROG, RAID type) and select four kinds of program(IOBENCH, LINPACK, QSORT, TPC-D) for proving the function of pgage. By experimental approach, pgage can easily detect the overall performance of the large scaled system especially and can give a guideline for system tuning of large scaled system in real environment.
