A storage area network has one or more digital data processors, e.g., hosts, in communication with one or more storage devices. At least a selected one of the hosts has an operating system in which a storage device must be claimed before the storage device can be accessed by applications programs executing on that host. The improvement is characterized by a selectively actuable filter, e.g., loaded with the selected host operating system, that when downloaded and actuated to a host intervenes to block claiming of one or more selected storage devices.