A technique for recalling data objects stored on media. A queue is created for
each medium on which data objects are located, where each request to recall a data
object is placed on the queue corresponding to the medium on which the data object
is located. A queue is "active" when its corresponding medium is mounted and being
used for recall; otherwise the queue is "non-active." A thread is created for each
active queue, where the thread retrieves from a medium the requested items on the
active queue. When plural drives are available for mounting and reading media,
plural queues may be active concurrently, so that the plural queues' respective
threads may recall items from the plural media in parallel. Preferably, the requests
on each queue are organized in an order such that the offset locations of the requested
items form two monotonically increasing sequences.
