A main data storage system has a main computer-implemented storage control and data storage, and a user interface, the main storage control in communication with a local computer-implemented storage control of a local data storage system with local data storage. In response to a request to increase data storage from the user interface, the main storage control determines whether the main data storage is out of space. If so, the main storage control sends a command to the local storage control to create data space in local data storage. The local storage control creates the data space and associates the data space with the main storage control; and, in response to a command from the user interface to rebalance data storage, the local storage control sends the command to the main storage control to search for storage space sufficient for the data space in the main storage.