SINGLE BULK PACK WD Red 5 TB WD50EFRX NAS Hard Drive: 3.5-inch SATA 6 IntelliPower 64 MB cache 3 Year Warranty WD Red is designed specifically for small NAS systems that have 1 to 8 drive bays. The drives are designed and extensively tested for compatibility in the unique 24x7 operating environment and for the demanding system requirements of home and small office NAS.