A method for managing storage space in a storage port queue includes establishing a watermark for the storage port queue. The method further receives, at the storage port associated with the storage port queue, a command having an initiator-target-LUN (ITL) nexus associated therewith. Upon receiving the command, the method determines whether the used space in the storage port queue has reached the watermark. In the event the used space has not reached the watermark, the method processes the command. In the event the used space has reached the watermark and a specified number of commands for the ITL nexus are already present in the storage port queue, the method rejects the command. Otherwise, the method may process the command. A corresponding apparatus and computer program product are also disclosed herein.