Patent ID: 7496724

Claim:
A storage system, comprising: a primary volume provided as an operational volume to a host computer; a secondary volume operable to form a copy-pair with said primary volume; and a storage controller operable to execute I/O processing respectively to said primary volume and said secondary volume in response to an I/O request issued from said host computer; wherein, if a load demanded for executing I/O processing to said secondary volume set with a second tuning parameter is lighter than the load demanded for executing I/O processing to said primary volume set with a first tuning parameter, said storage controller is operable to switch the primary/secondary relationship between said primary volume and said secondary volume and provide said secondary volume as the operational volume to said host computer, if the load demanded in executing I/O processing to said secondary volume is lighter than the load demanded in executing I/O processing to said primary volume during a certain period of time, said storage controller is operable to switch the primary/secondary relationship between said primary volume and said secondary volume and provide said secondary volume as an operational volume to said host computer, and if the load demanded in executing I/O processing to said primary volume is lighter than the load demanded in executing I/O processing to said secondary volume during other periods of time, said storage controller is operable to switch the primary/secondary relationship between said secondary volume and said primary volume and provide said primary volume as the operational volume to said host computer.