Since the threshold excess is judged by a value of high-workload IO of backup that is designed on the assumption that the workload of storage is high, whether the performance limit has been reached remains uncertain. Furthermore, although an optimistic prediction trend with low workload trend and a pessimistic prediction trend with high pessimistic workload trend are presented, LUs that require improvement remain uncertain. Moreover, the time to improve the configuration and the effect of the improvement remain uncertain. To improve the configuration, configuration information, performance information, and operation information are acquired from storage, a performance limit excess time is predicted based on the performance information excluding LUs exceeding the performance trend, and an optimal improved configuration is determined from the performance limit after improvement and the time required for the improvement.