METHOD AND APPARATUS FOR HANDLING AUDIT REQUESTS OF LOGICAL VOLUMES IN A VIRTUAL MEDIA SERVER

In a data storage subsystem a virtual removable media server (VRMS) handles host audit requests, whether directed to a physical volume or a virtual volume physically stored in cache or in a removable physical media item. The subsystem includes a storage interface between the host and data storage facilities including a cache and a physical media library. To the host, the storage interface emulates a virtual library including a plurality of virtual media items, each containing a logical volume of data. The library may also maintain physical media items each storing one logical volume, as in a traditional library. To verify presence of a specified logical volume of the virtual library, the host sends an audit request. Responsively, the subsystem cross-references the specified logical volume in a first list to identify physical locations of underlying data. This physical location may be an address in the cache and/or a physical volume corresponding to a physical media item in the library. If the underlying data is stored exclusively in cache, the subsystem automatically answers affirmatively to the audit request. If the underlying data is stored in the physical media, the subsystem searches the library for the physical media item containing the physical volume that includes the specified logical volume, and answers the audit request affirmatively if the physical media item is found. If the physical media item is not found, the subsystem answers the audit request negatively.