System using priority data of a host recall request to determine whether to release non-volatile storage with another host before processing further recall requests

Abstract

Disclosed is a system for handling recall requests for data maintained in a storage device accessible to multiple systems. Initially, a storage device is allocated to the first host system to process recall requests in a recall queue including a plurality of recall requests. A second host recall request is initiated with the second host system to recall data from the storage device. The second host system determines whether the storage device is allocated to the first host system. If so, the second host systems stores priority data in a common or shared data structure indicating a priority of the second host recall request after determining that the storage device is allocated to the first host system. The first host system then conditionally releases the storage device before processing all the recall requests needing the subject tape in its queue to make the storage device available if the priority in the common data structure is higher than its own highest priority request. The second host system retries the second host recall request after the first host system releases the storage device. The second host system then determines whether the storage device is available and whether the highest priority second host recall request is greater than or equal to the priority data indicated in the data structure when retrying the second host recall request. The storage device is allocated to the second host system to process the second host recall request after determining that the storage device is available and that the priority of the second host recall request is greater than or equal to the priority data indicated in the data structure.