Token State Recovery

· If a File Exporter is restarted (for example, after its File Server machine crashes), it loses all knowledge of the tokens it granted prior to the restart. For a brief period after it first returns to service, the File Exporter refuses all requests for new tokens from all clients, accepting requests only to reestablish tokens from those clients that held them before the File Exporter became unavailable. This is the first form of token state recovery.

· If a network failure prevents a client from contacting a File Exporter, the client may be unable to prevent its host lifetime from expiring. Once communications are restored, the client must either reclaim its tokens or, if necessary, request new ones. This is the second form of token state recovery.

· If a client is restarted, it loses all knowledge of the tokens it possessed prior to the restart; recovery of its tokens is not possible.

During the first form of token state recovery, the File Exporter attempts to preserve the state of its tokens across restarts by initially accepting requests only to reestablish existing tokens. While the File Exporter is unavailable, clients that have tokens from it continue to probe it at regular polling intervals until it returns to service. When it is again available, the File Exporter enters token state recovery to give these clients the opportunity to recover their tokens without threat of conflicts with tokens that were granted to new clients.

Different File Exporters remain in token state recovery for different lengths of time after a restart. However, each File Exporter ensures that its recovery period lasts long enough to give all of its clients the opportunity to reestablish their tokens, basing the duration on the host lifetimes or polling intervals that it assigns, whichever are greater.

During the second form of token state recovery, the File Exporter does not provide the client with an opportunity to reestablish its tokens without fear of conflicting tokens. The client continues to poll the File Exporter until the network outage is resolved. However, if its host lifetime expires before it can contact the File Exporter, the client may be unable to recover tokens that it held prior to the network problem.

Values that the File Exporter uses to determine the host lifetimes, host RPC lifetimes, and polling intervals of its clients are specified with options of the fxd command. (See Part 2 of this guide and reference for complete information about the fxd command and its options.)