GFS Consistency Model

GFS provides a custom consistency model for write operations.

The state of a file region after a mutation depends on the type of mutation, whether it succeeds or fails and whether there are concurrent mutations.

Note: A file region is consistent if all clients will always see the same data, regardless of the replica they read from.

A region within a file

A region is defined after a file data mutation if it is consistent and clients will see what the mutation writes in its entirety.

A region can be:

• Defined and consistent: When a mutation succeeds without interference from concurrent writes, the affected region is defined. All clients will always see what the mutation has written.
• Undefined but consistent: Concurrent successful

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