1. A method of operating a cluster of computer system nodes sharing direct read/write access to storage devices via a storage area network, comprising: requesting a token by a client node from a metadata server node for a file prior to performing a required access to the file; waiting for a response to said requesting; holding the token at the client node upon receipt from the metadata server node; releasing the token at the client node upon completion of the required access to the file; interrupting said waiting to check on status of at least one of data and node availability in response to detection of a change in location of the metadata server; receiving an instruction to detarget requests for the metadata server; receiving an instruction to retarget requests for a new metadata server; receiving a token recall request at the client node from the metadata server prior to the change in location; processing partial results at the client node upon receipt of the token recall request; releasing the token to the new metadata server in response to the change in location.