1. A storage system, which receives an I/O (Input/Output) request specifying a logical address of a logical storage area from a higher-level apparatus, comprising: a RAID (Redundant Arrays of Inexpensive Disks) group comprising multiple physical storage devices; and a storage controller, which, in accordance with the I/O request from the higher-level apparatus, sends an I/O command to a target physical storage device, which is an I/O-destination physical storage device in the RAID group, each physical storage device comprising: a physical area, which is regarded as the basis of the logical storage area; and a device controller, which is coupled to the physical storage area, and executes internal processing, which is processing executed without receiving a command from outside of the physical storage device, wherein a physical storage area state changes in accordance with the input/output of data to/from the physical storage area, the device controller inside the target physical storage device: (a) executes data I/O processing with respect to the physical storage area in accordance with the I/O command from the storage controller; and (b) subsequent to executing the I/O processing in the (a), sends to the storage controller a response with respect to the I/O command, this response comprising status information, which is information denoting a state of the physical storage area subsequent to being changed in accordance with the I/O processing, the storage controller: (A) receives the response from the target physical storage device; and (B) based on the status information included in the response received in the (A), makes a determination as to whether or not to execute the internal processing, and in a case where the result of the determination is to execute the internal processing, sends to the target physical storage device an internal processing execution command instructing to execute internal processing, and the device controller in the target physical storage device: (c) upon receiving the internal processing execution command, executes internal processing in accordance with the internal processing execution command.