In an environment in which plural external storage devices having different function
control interfaces are intermixed, when a function of a storage device is controlled
from a computer, a common interface for controlling the function of the storage
device is provided. A device that provides the common interface manages an interrelationship
between a storage area recognized by a host computer and a storage area provided
by the storage device and associates a storage area which becomes a target of a
function control instruction with the storage device that provides the storage
area. A type of the storage device that provides the storage area which becomes
the target of the function control instruction is identified and function control
is ordered through a function control interface unique to the device.