US Patent 7447837 Control device for a RAID device

A control device for a RAID device is provided which changes, when one or more disks are added, allocation of segments to existing stripes, each of which have created by use of existing disks, by use of the one or more disks to be added without changing the number of segments that constitute each stripe. The control device obtains one unallocated segment from each of disks, each of which is selected from the existing disks and the one or more disks to be added, the number of disks is equal to the predetermine number of segments to create a stripe. Then the control device creates a new stripe to which the obtained unallocated segment is allocated.