Virtual tape device and control method of virtual tape device

A control method of a virtual tape device, comprising:

• causing the virtual tape device to read, from a storage unit, logical volume information of a plurality of logical volumes, the logical volume information including, for each respective one of the plurality of logical volumes, an identifier of the respective logical volume, an updated time of the respective logical volume, information indicating whether the respective logical volume exists on a cache, an identifier of a respective physical volume storing data of the respective logical volume, and information indicating whether the respective physical volume is mounted in a physical tape drive or not;
• determining, based on the logical volume information, whether a requested logical volume exists on the cache when the virtual tape device receives a request to store the requested logical volume on the cache and whether a logical volume, being updated and stored in the physical volume mounted in the physical tape drive, exists on the cache when the cache does not have available capacity;
• causing the virtual tape device to select, based on the result of the determination, the logical volume information, and a determination that the requested logical volume has been read onto the cache from the physical volume at least a predetermined number of times, as a target logical volume to be offloaded from the cache, a logical volume of the plurality of logical volumes updated at an earliest time among logical volumes that exist on the cache;
• and
• causing the virtual tape device to offload the selected target logical volume from the cache.