Patent ID: 7743205

Claim:
A data storage system for storing data for at least one host computer, the data storage system comprising: a set of multiple read/write drives; a set of multiple data storage media slots wherein each data storage media slot receives a removable tape cartridge or removable disk cartridge; at least one robot that moves a tape or disk cartridge between one of the data storage media slots and one of the read/write drives; at least one library controller coupled to the robot and the data storage drives; non-removable data storage, wherein the non-removable data storage includes hard disk data storage, semiconductor memory data storage, or both, and wherein the non-removable data storage has a current memory capacity; at least one library management unit coupled among the at least one host computer, the non-removable data storage, and the library controller, wherein the library management unit: assigns a first set of virtual tape or disk cartridges whose associated data is stored on the non-removable data storage; assigns a second set of open tape or disk cartridges as being for indirect use by the host computer wherein data read from or written to a tape or disk cartridge in the second set is determined by the host computer; assigns a third set of closed tape or disk cartridges for use not by the host computer, but by the library management unit, wherein the third set of tape or disk cartridges supplement the current memory capacity of the non-removable data storage; and receives at least first, second and third tape or disk cartridges newly imported to the data storage system and: designates the first new cartridge as blank for use by the host computer or by the library management unit to write data to the first new cartridge, designates the second new cartridge for direct access by the host computer to permit the host computer to read and write data from the second new cartridge, and designates the third new cartridge as a cartridge having data to be stored on the non-removable data storage as a virtual cartridge, wherein the host computer accesses data on the third new cartridge from the non-removable data storage, but wherein the library management unit provides signals to the host computer to fool the host computer into responding as if the host computer were communicating directly with the third new cartridge, wherein said virtual cartridge is assigned a time-dependent residence priority defined by: a first duration of time said virtual cartridge remains inactive before being copied to removable data storage; a second duration of time said virtual cartridge is stored in said non-removable data storage, wherein said second duration of time is restarted on each access of said virtual cartridge; and a rate at which a priority for said non-removable data storage residence decays following said second duration of time.