Method of managing data in a data storage library

A method for managing data in a data storage library, and a data storage hierarchy suitable therefor, is disclosed. The data storage hierarchy includes an optical library and separate manually operated shelf storage. The optical library includes at least one optical disk drive and a plurality of storage cells for the storage of optical disks. The optical library also includes automatic means for transferring optical disks from the storage cells to the optical disk drives in the library. The host data processor, upon determining that particular data is required to be stored in the optical library, first checks to determine if the optical disks in the optical library currently have the capacity for the storage of such data. If the capacity exists in the optical library there is no problem and the data is stored therein. If the optical library does not have the required capacity, or if the system operator so requires, the optical disk in the optical library which has least recently been mounted on an optical disk drive therein is destaged from the optical library to the manually operated shelf storage. Another disk may then be fed into the optical library for the storage of the data required therein.