A storage system for continuing I/O without affecting drive box addition to a host computer includes: a plurality of drive boxes for connecting to a computer device that transmits commands for data reads or writes; and a storage controller connected to the drive boxes. A first drive box provides a first storage region to the computer device. The storage controller manages correspondence between the first storage region and a physical storage region of the drives constituting the first storage region. The first drive box receives a command for the first storage region from the computer device and transfers the command to the storage controller. The storage controller generates a data transfer command including a data storage destination based on the address management table, and transfers the command to the first drive box. The first drive box then transfers the data transfer command to the second drive box.