Abstract: A fault tolerant disk storage subsystem which includes a multipath dynamically alterable hierarchical arrangement of storage device controllers. Multiple storage device controllers are provided which are each adapted to emulate a storage device and which each include a cache memory which has multiple data input ports and multiple data output ports. A processing element within the storage device controller is utilized to selectively interconnect particular data input ports with selected data output ports to provide multiple paths within the storage device controller. An interconnection is then provided for coupling a data output port of one or storage device controller with a data input port of one more alternate storage device controllers which emulate storage devices, creating an alterable hierarchical arrangement of storage device controllers. Storage devices are then coupled to each of the lowest levels of the hierarchical arrangement of storage device controllers.