Amazon.com: WD 4TB 7200 RPM SATA 6 Gb/s 64MB Cache, 3.5-Inch Desktop Hard Disk Drive (WD4003FZEX) : Electronics
Amazon.com: WD Purple NV 4TB Surveillance Hard Disk Drive - Intellipower SATA 6 Gb/s 64MB Cache 3.5 Inch - WD4NPURX : Electronics
Amazon.com: WL 4TB 64MB Cache 5400RPM SATA III (6.0Gb/s) (Low Power & Heavy Duty) 3.5" Internal Hard Drive (PC, NAS & CCTV DVR) - w/ 1 Year Warranty : Electronics
WD Blue 4TB Desktop Hard Disk Drive - 5400 RPM SATA 6Gb/s 64MB Cache 3.5 Inch - WD40EZRZ - TechnoDeals USA