A RAID storage-device-assisted parity data update system includes a first RAID primary data drive that DMA's second primary data from a host system, and XOR's it with first primary data to produce first interim parity data for a first data stripe. A second RAID primary data drive DMA's fourth primary data from the host system, and XOR's it with third primary data to produce second interim parity data for a second data stripe. A first RAID parity data drive DMAs the first interim parity data and XOR's it with first parity data to produce second parity data for the first data stripe that overwrites the first parity data. A second RAID parity data drive DMA's the second interim parity data and XOR's it with third parity data to produce fourth parity data for the second data stripe that overwrites the third parity data.