An accurate evaluation system for disk array cache algorithms

The cache algorithm of a disk array is one of the key factors affecting its performance, and test and evaluation methods are of great importance to the design of effective cache algorithms. A cache algorithm evaluation system is designed to assess the performance of disk array cache algorithms. Based on the architecture and operation mode of the disk array, the system offers an environment model for cache algorithms evaluation, which includes four parts, i.e., the generating and queuing module for I/O operations, the cache algorithm slot module, the prefetching algorithm module and the disk simulator. The first module is able to generate a variety of I/O work loads and to replay I/O work loads of real systems; the second module is used to load cache algorithms to be assessed; the third module simulates the prefetching algorithm and I/O operation gathering of the disk array; and the disk simulator adopts DiskSim to ensure the measurement accuracy of I/O operation response time. With this system, the hit rates of cache algorithms and their influences on the average response time of I/O operation can be measured. To confirm the system's validity, it is employed to evaluate the hit rate and average response time of the I/O operation of the least recently used (LRU) algorithm. The test results are in good agreement with the results reported in the open literature, indicating the reliability and feasibility of the system.