A main data storage system has a main storage control and data storage, and a user interface, the main storage control in communication with a local 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 control determines whether the main data storage is out of space. If so, the main control sends a command to the local control to create data space in local data storage. The local control creates the data space and associates the data space with the main control; and, in response to the local control creating data space in the local data storage and notifying the main control, the main control updates its metadata with respect to the data space, creating the impression that all the data is stored in the main data storage.