Performance Evaluation for Memory Subsystem of Hierarchical Disk-Cache

The memory subsystem hierarchical disk-cache (MESSIAH) discussed in this paper aims at realization of high-speed access to secondary memory. MESSIAH uses a large-capacity buffer memory (A) for the input-output device and a small-capacity buffer (B) for each disk-device. (A) realizes the traditional disk-cache function. (B) realizes reduction of the disk-rotations waiting time due to a miss in RPS (rotational position sensing), reduction of overlap between disk write-in and search time, and immediate delivery of look-ahead data. In other words, in MESSIAH (A) realizes a cache memory of sufficient capacity and (B) copes with RPS misses, which increase with size of the transfer block between disk and (A). (B) also realizes high-speed write-in and read-out of the disk. Thus, MESSIAH provides greater advantage than the multiple effects of disk-cache function and the B-disk (buffer-installed disk device). This paper proposes an architecture for MESSIAH and verifies its usefulness by simulation.