Recent advances of the network medium and growing demand for higher data storage has led to the development of the shared storage distributed file system. In the shared storage distributed file system, client computers directly access the shared storage instead of sending messages to a server hosting the storage. This architecture maintains consistency of data through locking mechanism using some set of designated lock servers. Among many possible failures in a distributed file system, communication omission failure is taken care of by the use of lease mechanism. Lease allows lock servers to reclaim the locks given to the partitioned clients after some predefined time period. Data consistency is maintained, but the usefulness of the lease stops there. Partitioned clients can not make any progress until the system recovers from the network partition. This paper addresses this limitation and proposes a protocol that allows the partitioned clients to make progress even under the situations of the network partition. It is named as a rotational lease because the mechanism works in a manner that rotationally gives to each participating client a predefined lease term within which the client is allowed to modify the data at will. It is also shown that the proposed mechanism always preserves the data consistency.
