Amazon.com: Western Digital WD40EFRX WD Red NAS Hard Drive - Hard drive - 4 TB - internal - 3.5 inch - SATA 6Gb/s - buffer: 64 MB - for WD My Cloud EX2, EX4 : Electronics
WD Red 4TB NAS Hard Disk Drive - 5400 RPM Class SATA 6Gb/s 64MB Cache 3.5 Inch - WD40EFRX - Walmart.com
Western Digital Updates Red NAS Drive Lineup with 4 TB and 2.5" Versions
Amazon.com: Western Digital WD40EFRX WD Red NAS Hard Drive - Hard drive - 4 TB - internal - 3.5 inch - SATA 6Gb/s - buffer: 64 MB - for WD My Cloud EX2, EX4 : Electronics
The Western Digital Red 4TB NAS Drive Speed Test with Black Magic – WD40EFRX – NAS Compares
Amazon.com: Western Digital Red Pro 4TB 3.5-Inch 7200rpm 64MB Cache NAS Hard Drive (WD4002FFWX) : Electronics
WD Red Plus 1TB NAS Hard Disk Drive - 5400 RPM 3.5" - Newegg.com