Research And Optimize On Prfeftching Coorination Of Networked Storage System

With the development of network technology and introduction of concept of cloud computing, users have put forward higher requirements in performance and security of storage system. Recently, cloud storage has become a new area that the storage vendors joined. In order to improve the performance of storage system, storage providers are using a large buffer as caching in both client and server. However, as hardware upgrades, the capacity of cache is increasing, the performance of storage system is not increasing, or decreasing in sometimes. Researches show that there are two reasons limit the effectiveness of the multi-level cache architecture. First, with the increase of cache capacity, the hit rate in storage client is increasing, then, the requests sent to server has poor temporal locality. This result in the algorithms based-locality such as LRU has a lower utilization. Second, the large amount of data was stored client-side and server-side. These redundant data made the whole system performance lower than the total amount of caches in the hierarchy should be demonstrated. So, how can improve the utilization of cache space become the most extensively studied problems.The paper makes a research on the storage system. The results show that the prefetching algorithm applied to multi-level storage system is the algorithm that used in single system. These algorithms directly applied to multi-level storage system also brings a lot of limitations, such as overly conservative prefetching algorithm will not be able to effectively use the lower-level cache space, while overly aggressive prefetching algorithm will be compounded across levels and generate large amounts of wasted prefetch. Thus wasting a lot of storage space. Prefetching coordination algorithm can improve the utilization of L2 Cache by analyzing the mode of the requests and forecasting the state of L2 Cache. And it does not change the original prefetching algorithm. Based on a detailed analysis to the current prefetching coordination algorithm, the thesis found two problems: first, it has little effect for the random request, and cannot improve the utilization of L2 Cache significantly. Second, it can only be worked with homogeneous combinations of prefetching algorithms at multiple levels.For the two defects of perfetching coordination algorithm, the thesis put forward a new improvement algorithm. It can not only improve its efficiency in the random request, can also be used in heterogeneous storage systems architecture. In order to validate the improved coordination algorithm, this thesis designs and implements a two-level storage system test bed, and uses different prefetching algorithm in it. The results show that the new algorithm can improve the performance of storage system in both random and sequential requests. It can be used in heterogeneous system environment, and the performance of this kind of heterogeneous system depends almost entirely on the prefetching algorithm that used in server side. Prefetching coordination algorithm provides a new method in improve the performance of storage system, and does not require any additional cost. So, it has very important theoretical and practical value.