1. A first storage system coupled to a second storage system, a computer and a name server, the first storage system comprising: a first port coupled to the computer via an IP network; a plurality of disk drives on which a first volume is constructed; and a processor, coupled to the first port and the plurality of disk drives, which assigns the first volume to the first port, receives, directly from the second storage system without being passed through the computer, a target name that is used in the second storage system, assigns the target name to a set of the first port and the first volume in the first storage system, and sends information of the target name to the name server when a data migration from the second storage system directly to the first storage system is executed, wherein the name server notifies the computer of the information of the target name after receiving notification of the target name from the first storage system by using the iSCSI protocol, wherein the first port accepts an access request from the computer to the first volume after sending the information of the target name to the name server by using an iSCSI protocol if the access request includes the target name, and wherein the first storage system receives accesses from the computer to the first volume instead of a second volume in the second storage system based on the target name after executing the data migration and after the computer receives notification of the target name from the name server by the iSCSI protocol, whereby neither an operating system of the computer nor an application operating on the computer acknowledges the data migration from the second storage system to the first storage system.