1. In a storage area network (SAN) comprising one or more digital data processors in communication with one or more storage devices, wherein at least a selected one of the digital data processors operates under an operating system having a port driver defining a software interface between a class driver and an adapter to which one or more of the storage devices are coupled, a class driver for claiming a storage devices for access by the operating system and any applications programs executing therein by invoking the port driver to which such device is coupled, the improvement comprising: a filter in communication with the port driver and the class driver, the filter intervening to block claiming of one or more selected storage devices by the class driver.