1. A storage system comprising: a host computer; at least one storage device including disk units and a controller, which provides a logical volume to the host computer based on the disk units and a storage function; a management server storing storage function management information indicating that the at least one storage device provides the storage function, wherein the management server: (A) receives a system request input; (B) decides that the system request input is satisfied by the provided storage function, based on the storage function management information; (C) if the system request input is not satisfied, selects an validate candidate storage function and a validate candidate storage device which is one of the at least one storage device, for satisfying the system request input by validating the validate candidate storage function to the validate candidate storage device; and (D) in response to the system request input, displays an identifier of the validate candidate storage function and an identifier of the validate candidate storage device as a required function for satisfying the system request input.