1. A method for issuing a partition balancing subtask, applied to a controller, wherein the controller and at least two nodes form a storage system, and wherein each node comprises a partition, the method comprises: generating a second partition balancing subtask set after a second partition balancing task is received, wherein the second partition balancing subtask set comprises a partition balancing subtask, and wherein the partition balancing subtask records: a migration partition, a node to which the migration partition belongs, and a destination node; searching a current partition balancing subtask set; deleting a repeated partition balancing subtask between the second partition balancing subtask set and the current partition balancing subtask set; and issuing the partition balancing subtask in the second partition balancing subtask set after the repeated partition balancing subtask is deleted to the destination node recorded in the partition balancing subtask.