Metadata

Let's explore how GFS manages the filesystem metadata.

The master stores three types of metadata:

1. The file and chunk namespaces (i.e., directory hierarchy).
2. The mapping from files to chunks.
3. The locations of each chunk's replicas.

There are three aspects of how master manages the metadata:

1. Master keeps all this metadata in memory.
2. The first two types (i.e., namespaces and file-to-chunk mapping) are also persisted on the master's local disk.
3. The third (i.e., chunk replicas' locations) is not persisted.

Let's discuss these aspects one by one.