Amazon.com: WD Black 4TB Performance Desktop Hard Disk Drive - 7200 RPM SATA 6 Gb/s 64MB Cache 3.5 Inch - WD4001FAEX : Electronics,Western Digital Red Pro 4TB 3.5-Inch 7200rpm 64MB Cache NAS Hard Drive (WD4002FFWX) : Electronics - Amazon.com,Western Digital Red Plus (5400RPM, 3.5,Western Digital 4TB WD Red Plus NAS Internal Hard Drive HDD - 5400 RPM, SATA 6 Gb/s, CMR, 64 MB Cache, 3.5