A SAN manager acquires information which each unit manages from a management agent of each unit connected to a SAN, detects virtual volume mapping and real volume mapping in the SAN based upon the acquired information and manages them. A SAN management server holds an event translation dictionary for translating contents of a failure notification message received from each unit in the SAN and detects an effect which failure has upon I/O access of a virtual volume if a failure notification message is received. Further, a function for checking a request for generating a virtual volume from a SAN administrator based upon virtual volume mapping information and real volume mapping information is realized.