Tiered storage system configured to implement data relocation without degrading response performance and method

An information storage system comprising:

• a plurality of physical storage drives different in performance for providing real storage areas to a pool which is tiered into a plurality of tiers different in performance;
• and
• a controller,
• wherein the controller monitors accesses to a first tier in the pool;
• wherein the controller determines a loaded state of the first tier based on the accesses to the first tier;
• wherein the controller holds management information relating loaded states of the first tier to relocation speeds and/or modes of moving data in data relocation between a second tier in the pool and the first tier;
• and
• wherein the controller determines at least one of a relocation speed and a mode of moving data in data relocation between the second tier and the first tier based on the determined loaded state of the first tier and the management information;
• wherein the controller holds results of the monitoring accesses to the first tier and information indicating relations between access frequencies in the first tier and response performance values to a host;
• and wherein the controller estimates effects of degradation in response performance to the host caused by relocation at a plurality of different relocation speeds with reference to the results of the monitoring and the information indicating the relations and selects a new relocation speed from the plurality of relocation speeds based on the estimated effects.

A method of controlling an information storage system including a plurality of physical drives which are different in performance and provide real storage areas to a pool, the pool being tiered into a plurality of tiers different in performance, the method comprising:

• monitoring accesses to a first tier in the pool;
• determining a loaded state of the first tier based on the accesses to the first tier;
• holding management information relating loaded states of the first tier to relocation speeds and/or modes of moving data in data relocation between a second tier in the pool and the first tier;
• and
• determining at least one of a relocation speed and a mode of moving data in data relocation between the second tier and the first tier based on the determined loaded state of the first tier and the management information,
• wherein the controller determines degrees of improvement in access performance by relocation at different relocation speeds based on numbers of pages that can be relocated at the different relocation speeds, access performance of the first tier and access performance of the second tier, and
• wherein the controller selects a new relocation speed from the different relocation speeds based on the determines degrees.