An information processing system including a processor, a memory, and a plurality of drives, wherein when a write request of new data is received, the processor stores the new data in the memory, transmits a response for the write request to a transmission source of the write request, reads old data updated by the new data from a first drive of the plurality of drives and old parity related to the old data from a second drive of the plurality of drives according to transmission of the response, store the old data and the old parity in the memory, generates new parity related to the new data from the new data, the old data, and the old parity stored in the memory, and stores the new data in the first drive to store the new parity in the second drive.