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Amazon.com: Western Digital 4TB WD Red NAS Internal Hard Drive HDD - 5400 RPM, SATA 6 Gb/s, SMR, 256MB Cache, 3.5" - WD40EFAX : Electronics
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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
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