Abstract: To balance the demand for high-speed process and large storage capacity,computer storage hierarchy is a typi-cal pyramid-shaped structure.However,as the information technology develops rapidly,the speed gap between computerprocessor and disk has been widened,which makes the disk access become the bottleneck of the computer system.In recent decades,how to reduce the impact of I/O delay has been a hot issue in storage fields.Prefetching,namely predicting I/O requests in advance and reading the data into cache to hide I/O delay behind application,is a vital technique to alleviate the bottleneck.DiskSeen is a block-level prefetch policy.It can improve the sequential access of disk and prefetching performance by analyzing the relationships between the blocks’ locations and access times.Based on DiskSeen,the following work was done in this paper.First,based on the drawbacks of DiskSeen,we proposed dynamic control for prefetch size and active history-aware prefetch in second match to optimize the efficiency.Secondly,we realized DiskSeen algorithm and the optimization of it.Lastly,we conducted comparison test in a simulation environment.The results show that DiskSeen can effectively increase hit ratio and reduce average response time.Furthermore,our optimization can further improve system performance on above two aspects.

Key words: Storage system,Prefetching,I/O delay,DiskSeen,Optimization