Abstract: A system for optimizing the position and use of cartridges of machine-readable data storage media in an automated super library. The invention is implemented in a super library that includes a main library bin with a plurality of cartridge slots, a picker, and multiple small libraries, where each small library has a small library bin with multiple slots, a picker, and at least one data drive. Mount queue times are estimated for each small library, and a main library picker is selectively operated to transfer cartridges between the small libraries based on the estimated mount queue times. This provides expedited access of the cartridges at the small libraries. The host processor maintains requests for such inter-library transfers in a main picker queue, for processing by the main picker. When each small library has a non-empty mount queue, the main picker processes small libraries' cartridge transfer requests by efficiently distributing cartridges along the small libraries.