PERFORMANCE EVALUATION FOR BUFFER-CONTAINED DISK UNITS.

The rotation delay of a disk caused by RPS-miss, which is larger than usually assumed, is nonnegligible in systems of heavy load. A method is proposed to cope with this delay by improving the response time and throughput: a buffer-contained disk unit. Its performance evaluation is shown by simulation. The buffer-contained disk unit has a small amount of buffer (some tens of kB). Data transmission between a buffer and a disk control unit and disk rotation occur asynchronously, which considerably reduces the delay time. In writing operation, the seek time is overlapped by data transmission time, and seek and rotation delay time appear to be zero. In simulation, an access pattern of real system is used which is obtained by tracing the disk input/output operation. Hence, the response and throughput are clearly improved. The method can be applied to a large variety of disks with great performance improvement and little add-on hardware.