SINGLE BULK PACK WD Red (WD30EFRX) is the only hard drive designed for NAS systems that have 1-5 drive bays. The drives are designed and extensively tested for compatibility in the unique 24x7 operating environment and demanding system requirements of home and small office NAS. 3TB, SATA 6Gb/s, 64MB cache, IntelliPower Rotational Speed.