According to one embodiment, a data storage apparatus includes a write command module, a read command module, and a controller. The write command module is configured to process a write command for writing data to the nonvolatile memories for a plurality of channels, respectively. The read command module is configured to process a read command usually and to process a read command for read modify write (RMW) operation. The controller is configured to control the read command module, causing to execute the read command for the RMW operation, prior to the normal read command, thereby to execute a flush command, and to control the write command module, causing to execute a write flush process that includes the processing of a write command for the RMW operation after the read command for the RMW operation has been executed.