磁盘阵列Cache算法精确测评系统研究

磁盘阵列Cache算法的优劣是决定磁盘阵列性能的关键因素之一,精确的测试和评估方法对设计高效率的Cache算法至关重要.为了精确评估磁盘阵列中Cache算法的性能及其对系统I/O性能的影响,设计了一个Cache算法测评系统.依据磁盘阵列的系统构成和运行模式,建立了评估Cache算法的运行环境模型,包括I/O操作的产生和排队模块、Cache算法插槽模块、预取算法模块和磁盘模拟器4个部分.其中I/O操作的产生和排队模块能够产生多种形式的I/O操作负载及重放实际系统的I/O操作负载;Cache算法插槽模块用来挂载待评估的Cache算法;磁盘模拟器采用DiskSim,保证了测量磁盘I/O操作响应时间的精确性.系统能够精确测量Cache算法的命中率,以及对存储系统I/O操作平均响应时间的影响.实际测量了LRU算法的命中率和I/O操作平均响应时间,测量结果与既有的研究成果相吻合,从而验证了系统的性能.因此,系统具有良好的可靠性、可用性和可扩展性.

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.