SINGLE BULK PACK WD Red Pro 2 TB WD2001FFSX NAS Hard Drive: 3.5-inch SATA 6, IntelliPower, 64 MB cache, 5 Year Warranty WD Red Pro is designed specifically for medium to large NAS systems that have up to 16 drive bays. The drives are designed and extensively tested for compatibility in the unique 24x7 operating environment and for the demanding system requirements of medium to large NAS.