To provide a storage apparatus in which a plurality of drives in a unit are separately treated and the unit can be easily exchanged for another unit even when RAID groups are freely composed. The storage apparatus includes a plurality of drive cases in each of which a plurality of units are detachably mounted, each of the units including a plurality of drives that are detachably, and a controller case in which a disk control section is provided, wherein the disk control section comprises a RAID group creation section for creating a RAID group using the plurality of disks and an exchange indicating section for giving a notice that a unit is ready to exchange after rebuilding or copying of data in disks included in the unit at the time of exchange of the unit.