The metadata are in the master service which is a custom database. It must be updated when an object is written and read must lookup this database to figure out on which volume to get the data.

The metadata database is a implemented in seaweedfs. It is strongly consistent (Raft), meaning that the leader handles all writes and acknowledges an update once all running servers have a copy. Reads can be from any servers.

The test coverage is unclear and appears to be low. There does not seem to be integration tests.