Abstract: A method and system for reassigning unused logical volumes on a storage subsystem to an open systems host that uses logical unit numbers (LUNs). The storage subsystem and the open systems hosts execute respective software processes, and the open systems host is connected to a storage subsystem via an adapter that is controlled from a support controller. The method and system include sending a communication message from the support controller to the adapter, wherein the communication message reassigns the unused logical volumes to LUNs. The method and system further include updating a logical-to-physical mapping stored within the adapter in response to receiving the communication message, whereby storage capacity of the open systems host is increased without suspending the software processes.