Abstract: A data storage system is constructed to rapidly respond to a physical backup request for backup of a physical storage unit such as a disk volume or cylinder. A user, however, may request backup of a logical data structure such as a file having a rather complex mapping to a number of physical storage components such as a number of disk tracks. For backup and restore of such a logical data structure, a backup agent requests an application interface routine to backup a physical storage unit that includes the logical data structure. The application interface routine issues a corresponding physical backup request to the data storage system, and creates a catalog of information about content of the physical storage unit that would be needed for restoring the logical data structure from the backup version of the physical storage unit.