The regular disk module simulates a portion of the HP97560 disk or the Seagate ST19101 disk, whose relevant parameters are shown in Table 1. A ramdisk driver is used to store file data using 24 MB of kernel memory. The Dartmouth simulator [17] is ported into the kernel to ensure realistic timing behavior of the HP disk. We adjust the parameters of the Dartmouth model to coincide with those of the Seagate disk to simulate the faster disk. Although not as accurate, the Seagate model gives a clear indication of the impact of disk technology improvements. We have run all our experiments on both disk models. Unless stated otherwise, however, we present the results obtained on the Seagate model.
The ramdisk simulator allows two simulation modes. In one mode, the simulator sleeps the right amount of time reported by the Dartmouth model and we can conduct the evaluations by directly timing the application. In the second mode, the simulator runs at memory speed without sleeping. This mode speeds up certain phases of the experiments whose actual elapsed time is not important. The disadvantage of the ramdisk simulator is its small size due to the limited kernel memory. We only simulate 36 cylinders of the HP97560 and 11 cylinders of the Seagate.