A storage subsystem capable of satisfying conditions such as storage capacity and access performance requested by users and to enable expansion of storage drives that are not in RAID group (RG) units is provided at a low cost. The storage subsystem includes a first storage drive for storing data sent from a host computer, a second storage drive having a property that differs from the first storage drive for storing data sent from the host computer, and a processor for controlling the first storage drive and the second storage drive, wherein a processor receives RG configuration requirements from the host computer and determines whether an RG satisfying the RG configuration requirements can be configured, and if the processor determines that an RG can be configured, the first storage drive and the second storage drive are combined to configure the RG.