Failure investigation in a SAN providing virtual volumes requires a high degree of knowledge from the SAN administrator, who also evaluates the relative severities of failure events from different devices. The SAN manager obtains information from management agents in the devices. Using this information, the SAN manager manages the association between the server and the virtual volumes and the real volumes. The SAN manager receives failure messages from multiple devices and uses the association and a failure analysis dictionary table to determine the contents of the failure messages and associations between failure messages. Failures that are causal failure are displayed. The SAN manager is equipped with a conversion table for converting failure messages issued from different storage devices to a common severity. When a failure message is received, a notification is sent to a high-level program and to an administrator based on the common severity defined in the conversion table.