Much of the past research on file migration and file replication has examined these two resource management strategies in isolation or in an environment where they do not work together. We establish through simulation that these two strategies can be utilized simultaneously to potentially provide significant performance benefits over a system without file migration or replication. File replication can be viewed as a natural extension to file migration, and thus, we derive a dynamic file replication policy based on an established file migration heuristic: a file is migrated (or replicated) whenever a reduction in total mean response time of the file requests currently in the affected storage sites can be achieved. Through our performance model, we use simulation to establish the conditions under which our file migration/replication policies are beneficial in a distributed file system.

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.>