Data paths

This section describes how file data gets from an application to the disks that hold it, and back.

The read path describes a read and its two exchanges: the client asks the Master Server which chunk holds the bytes and where its copies are, then fetches the data from a Chunkserver. The write path describes a write: the grant that the Master Server gives, the chain of Chunkservers that the data passes through, and the report that makes the change visible. Client cache and read-ahead covers what the client keeps in memory for both, and for how long.

The Master Server arranges these transfers but does not take part in them, so the traffic that these pages describe goes between clients and Chunkservers. The metadata paths describe what the Master Server does with its own state.