Research On Multi-Level Cache Policy Based On VISA System

In the era of Internet, people have designed and implemented Network Attached Storage systems, storage area networks and other network storage architecture. With the rapid development of the network technology, network bandwidth has gradually ceased to be a performance bottleneck of the network storage system. Instead the performance of I/O storage subsystem is playing an increasing role.At current study, researchers use Cache technology and prefetching technology as an important tool to improve the performance of storage subsystems. By now, researchers have designed and developed a lot of cache management and scheduling algorithm for a single computer system and DAS (Direct Attached Storage) System to achieve optimal performance. But in the network storage environment, storage systems and storage path structure have undergone great changes. These traditional cache management and scheduling algorithms are not suitable for the emerging network applications.VISA (Virtual Storage Interface Architecture) is one kind of distributed network storage systems which provides block interface. It uses vSCSI (VI-attached SCSI) as data transmission protocol which is based on VIA(Virtual Interface Architecture). According to the I/O characteristics of the network storage systems, a two-level cache for VISA is designed, and each level uses a different replacement strategy. In order to maximally use the space of two-level Cache, We design an algorithm named"R&E"and a kind of intelligent prefetching strategy for the second level cache, which can improve the access performance of VISA system effectively with negligible tradeoff.The entire system is running on Red Hat Linux 9.0 (kernel version 2.4.20) environment. Using IOzone and magnitude of the application of two types of storage Trace(Financial institutions online transaction procession and web search engine) as test tools, the results show that the two-level cache strategy for VISA system has played an important role on the performance promotion for some application.