Patent ID: 7711896

Claim:
A method for controlling a storage device to be coupled to an external storage device, said storage device comprising a protocol adapter and a cache adapter, said method comprising: a first determining step of whether said external storage device requires an input/output processing via cache adapter based on a request function level against said external storage device during logical unit path setting so that an input/output performance of said storage device is maintained; and if said input/output processing via said cache adapter is required for said external storage device, conducting said input/output processing to said external storage device via said cache adapter, and if said input/output processing via said cache adapter is not required for said external storage device, conducting said input/output processing to said external storage device not via said cache adapter, if said request function level is changed after said path setting, a second determining step of whether said external storage device requires an input/output processing via cache adapter based on said changed request function level against said external storage device during logical unit path switching, if said input/output processing to said external storage device is set said protocol adapter directly, and based on a result of the second determining step, changing access mode, which indicates a processing configuration of an input/output request to said logical unit, from said protocol adapter directly to via said cache adapter, and if said input/output processing to said external storage device is set via said cache adapter and based on a result of said second determining step, changing access mode from via said cache adapter to said protocol adapter directly, wherein said access mode is changeable while receiving input/output commands from a host computer, wherein said protocol adapter comprises a port receiving input/output commands from a host computer, one of said input/output commands requesting said input/output processing, wherein said cache adapter comprises a disk array, wherein said external storage device is to be coupled to said protocol adapter, and wherein said request function level designate information indicating whether or not functions of said storage device which is applied to said external storage device needs a process via said cache adapter.