Commissioning and decommissioning metadata nodes in a running distributed data storage system

A distributed data storage system comprising:

• a plurality of storage service nodes;
• at least one storage service node that executes a distributed barrier logic, wherein the distributed barrier logic is configured to control a commissioning of a second metadata node into the distributed data storage system without interrupting servicing of read requests from and write requests to any of the plurality of storage service nodes, and wherein the commissioning re-distributes ownership of a set of keys among metadata nodes in the distributed data storage system;
• a first metadata node configured to receive read requests and write requests for metadata that is associated with a first range of keys within the set of keys,
• wherein the first metadata node comprises a first storage service node that executes a metadata subsystem of the distributed data storage system,
• wherein the set of keys are unique identifiers that ensure strong consistency within the distributed data storage system,
• wherein each key of the set is owned by exactly one metadata node in the distributed data storage system,
• wherein the first metadata node:
• owns the first range of keys, and stores and maintains first metadata files at the first storage service node, and
• wherein each first metadata file is associated with the first range of keys;
• the second metadata node at a second storage service node that is distinct from the first storage service node, wherein on activation the second metadata node lacks metadata files associated with any of the keys in the set,
• wherein the second metadata node comprises the second storage service node that executes the metadata subsystem of the distributed data storage system, and
• wherein the second metadata node is configured to claim a second range of keys from the set, wherein the second range is part of the first range of keys owned by the first metadata node;
• and
• after the commissioning is complete, the second metadata node is further configured to receive read requests and write requests for metadata associated with the second range of keys, and
• wherein first metadata files associated with the keys of the second range are stored at the second storage service node and maintained by the second metadata node.