This product is either discontinued or we cannot get that from suppliers.
Western Digital Hard Drive (WD40EFRX), SATA 6.0Gb/s, 4TB, 5400 RPM, 64MB, Form Factor 3.5".
Western Digital 4TB, 64 MB, 3.5" WD Red NAS Hard Drive (WD40EFRX) WD Red drives with NASware 3.0 technology are purpose-built to balance performance and reliability in NAS and RAID environments.