Limited effects of finite storage on a beneficial file migration policy

Abstract

With the availability of high-speed local-area networks, file migration becomes an attractive option in a distributed file system. However, certain limitations may exist which restrict the movement of files. One such limitation is that storage space is finite and thus, storage sites (file servers) can only store a limited number of files. We use simulation to show that for a homogeneous distributed file system which transfers whole files, migrating files from congested to uncongested storage sites can result in significant performance gains over a system without file migration even in the case of finite storage. Our file migration policy is based on an instantaneous performance gain analysis: a file is migrated only if it leads to a decrease in the overall response time of the file requests currently in the system. Our results indicate that as the system load or coefficient of variation of the file request interarrival times increase, so does the percentage improvement of our file migration policy over a system without file migration. The degradation in performance caused by limited storage space is only significant when the storage restrictions are extreme.<>