Storage system and its logical unit management method

A logical unit management method for a storage system including:

• a plurality of storage devices configuring a RAID croup;
• a plurality of access-target logical units, each of which is a logical unit formed in a storage area of the plurality of storage devices and is an access target of an access requestor;
• a management-information logical unit that is a logical unit formed in the storage area of the plurality of storage devices and whose area for storing format management information for managing whether each of the access-target logical units has been formatted or not is divided into a former page area and a latter page area;
• and
• one or more controllers for controlling data input to, or output from, each logical unit and executing format processing on the access-target logical unit;
• the logical unit management method comprising, as steps executed by the controller when executing the format processing on the access-target logical unit:
• a step executed by the controller calculating a capacity of the format management information based on a capacity of each of the access-target logical units;
• a step executed by the controller calculating, according to a ratio of the calculated capacity of the format management information to a page management unit with a specified capacity, the number of management information pages necessary to manage the format management information using the page management unit;
• a step executed by the controller allocating part of the format management information for the plurality of access-target logical units, from among the format management information corresponding to the calculated number of the management information pages, to the former page area;
• a step executed by the controller allocating the remaining format management information for the plraulty of access target logical units, from among the format management information corresponding to the calculated number of the management information pages, to the latter page area by consierinq allocation of the plurality of access-target logical units in the RAID group;
• and
• a step executed by the controller storing an execution result of the format processing as the format management information in the former page area or the latter page area.