Storage system and capacity allocation method therefor

A storage system comprising:

• a plurality of drive devices that drive a plurality of physical disks each having a physical storage area;
• a RAID configuration unit that configures a plurality of RAID groups by grouping two or more of the physical disks;
• a logical disk creation unit that creates a logical disk on a given RAID group, the logical disk having a logical storage area associated with the physical storage area of the given RAID group;
• a memory for storing a RAID group control table comprising, for each RAID group, power status information for said each RAID group;
• a receiver to receive requests, wherein when the receiver receives a request for creating a new logical disk, a selected RAID group that is in a powered state is selected from among the plurality of RAID groups based on information comprising the RAID group control table;
• and
• an allocator configured to allocate to the new logical disk some of the physical storage area of the selected RAID group,
• wherein when the storage system receives a write request for the new logical disk, the storage system stores data associated with the write request on the physical storage area that is allocated to the new logical disk,
• wherein the allocation comprises a selector that selects, as the selected RAID group, a primary RAID group in the powered state having a free capacity that is largest among RAID groups in the powered state,
• wherein when the free capacity of the primary RAID group is greater than a requested capacity of the new logical disk, the physical storage area of the primary RAID group is allocated entirely to the new logical disk.