1. An apparatus for transferring objects between locations in a multi-dimensional storage array in response to n pending requests to transfer objects, where n.gtoreq.2, comprising: a robot for transferring said objects between locations in said storage array; and a library controller having: means for controlling said robot in response to the pending requests to transfer objects; and means for determining the shortest possible time to execute m pending requests, where 2.ltoreq.m.ltoreq.n, by considering the time to execute differently ordered sequences of the m pending requests.