Abstract: A data storage controller for controlling data storage in a storage environment comprising at least one of: a backend storage system of a first type in which data volumes are stored on storage devices physically associated with respective machines; and a backend storage system of a second type in which data volumes are stored on storage devices virtually associated with respective machines, the controller comprising: a configuration data store including configuration data which defines for each data volume at least one primary mount, wherein a primary mount is a machine with which the data volume is associated; a volume manager connected to access the configuration data store and having a command interface configured to receive commands to act on a data volume; and a plurality of convergence agents, each associated with a backend storage system and operable to implement a command received from the volume manager by executing steps to control its backend storage system, wherein the volume manager is configured