Abstract: A filter comprises a first device, a second device, a dynamic filter, and a device monitor. The dynamic filter is coupled to the first device and the second device, and selectively directs commands to the first device and to the second device based on dynamic status of the first device. The device monitor is coupled to the dynamic filter and to the first device and capable of determining the first device dynamic status.

Abstract: An apparatus capable of determining state of a device comprises a controller and a monitor executable on the controller. The monitor is capable of passively monitoring traffic between an initiator and the device, determining when the passively monitored traffic is insufficient for identifying state of the device, and actively issuing supplemental commands to the device to refresh device information when passively monitored traffic is insufficient. The monitor can also determine device state from the device information.

Abstract: An apparatus comprises a data path capable of coupling a physical device to a plurality of initiators. An interface is coupled to the data path and forms a command pathway between the plurality of initiators and the physical device. The controller is coupled to the data path and coupled to the interface. A controller comprises an executable process that creates a virtual device object that resolves conflicting concurrent attempts to access the physical device by a plurality of initiators. The virtual device object is capable of protecting state of the physical device during successive data transfer and media movement operations by emulating responses of the physical device and redirecting access to the physical device when the physical device becomes available.