A storage system that accepts an I/O command from a computer, comprising:
- a plurality of physical storage devices;
- and
- a controller managing a plurality of internal logical units on the plurality of physical storage devices and providing a plurality of external logical units to the computer, each external logical unit corresponding to at least one of the plurality of internal logical units,
- wherein the controller includes a memory storing a configuration management information which represents a free area and a free capacity in a storage space of each of the plurality of physical storage devices the free area is an address area occupied by a free space not used as the internal logical units, the free capacity is a capacity of the free space,
- wherein the controller accepts, from a management interface section that accepts information input by an operator using a console and displays information on the console, a logical unit expansion command including information designating a first external logical unit corresponding to a first internal logical unit and a first capacity input by the operator,
- wherein the controller specifies, in response to the logical unit expansion command, a first portion of the free space and a second portion of the free space in the free space in the plurality of physical storage devices based on the configuration management information,
- wherein the controller executes an internal logical unit creation process in which the specified first portion of the free space is defined as a second internal logical unit with a second capacity, the specified second portion of the free space is defined as a third internal logical unit with a third capacity, each of the second capacity and the third capacity is defined in accordance with the first capacity designated by the logical unit expansion command so that a total capacity of the first internal logical unit and the second internal logical unit and third internal logical unit is equal to the first capacity, additionally the configuration management information is updated to indicate that the first portion and the second portion of the free space occupied by the second internal logical unit and the third internal logical unit,
- wherein the controller executes, after the internal logical unit creation process is executed, an internal logical units combining process in which the first internal logical unit, the second internal logical unit and the third internal logical unit are correlated and corresponded to the first external logical unit and provided to the computer as the expanded-first external logical unit with the capacity equal to the fps first capacity designated by the logical unit expansion command,
- wherein the controller transmits, to the management interface section, information about a result of the processes executed in response to the logical unit expansion command, and
- wherein a capacity of each of the plurality of internal logical units is variable, and the first capacity of the second internal logical unit is different from the second capacity of the third internal logical unit.