SINGLE BULK PACK WD Red 6 TB WD60EFRX NAS Hard Drive: 3.5-inch SATA 6, IntelliPower, 64 MB cach. WD Red is designed specifically for NAS systems that have 1 to 8 drive bays in both 3.5-inch and 2.5-inch form factors. 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. Our enhanced dual-plane balance control technology significantly improves the overall drive performance and reliability. Hard drives that are not properly balanced may cause excessive vibration and noise in a multi-drive system, reduce the hard drive life span, and degrade the performance over time. (EFRX models only). 3 Year Warranty