Overview The increasing load of today's file servers prompts for a flexible storage design that can achieve dynamic load balancing across multiple storage units. To motivate the need for dynamic file migration, we are currently in the process of collecting traces from the NFS servers used in our department. In addition, the recent proposal of NFS 4.0 that includes file system migration, is another indication that migration is considered necessary in order to achieve load balancing. As a result, a file that belong to a certain virtual directory can freely migrate among any node that has a corresponding local directory that has the same pathname as the virtual one.
Virtual directories are volatile.
They are constructed on demand and discarded when not used for a long time. Since the file operations are ultimately performed on one of the corresponding local file system, the virtual directories can be reconstructed at anytime from the local ones. This allows the aggregated physical memory of the cluster to be equally used by any of the nodes for file caching. Our target application is a distributed NFS server. Spec SFS is used as the initial benchmark.