GFS Consistency Model and Snapshotting

Here we look at two things. First, how GFS keeps its operations and data consistent. Second, how it implements a snapshot.

GFS consistency model

GFS keeps its consistency model relaxed on purpose. It favors simplicity over strict guarantees.

Metadata operations, like creating a file, are atomic. They either happen completely or not at all. The master handles all of them by itself. Locking the right part of the namespace keeps each operation correct. The master's operation log is a running record of every metadata change. It gives all of them one global order.