US Patent 9760292 Storage system and storage control method

In executing a balancing process for moving data between a plurality of storage device groups constituted by a plurality of storage devices, a storage system determines whether or not to execute a balancing process for satisfying a first avoidance requirement for avoiding the occurrence of a problem in any one storage device only, on the basis of a second avoidance requirement which is satisfied by a second balancing process executed prior to a first balancing process for satisfying the first avoidance requirement, and executes the first balancing process in a case where the result of this determination is affirmative.