4TB HGST Deskstar NAS 3.5" Hard Drive 7200RPM HDN726040ALE614 (Refurbished)

I installed 2 of these in a Synology Network Attached Storage (NAS) Model 220j and later a NVR. -- GOOD PRICE/PERFORMANCE: I got them for the low price and the Hitachi reliability and the fact that Deskstar is an enterprise grade drive hence probably the reason they provide a 3 year warranty. -- CORRECT 4TB CAPACITY: Both drives only provide 3.6TB of storage vs the 4 TB advertised. Thats actually correct as that's how capacity is reported by hard drive manufacturers, but the underlying computer system reports in binary, hence the difference. -- WORKS IN NAS: While Synology stated these were not approved drives for their NAS, they work just fine in the NAS. -- NO ERRORS: The NAS did not report any errors on the drives during the drive configuration when is checks and the NAS takes many hours to verify the drives on initialization. -- STREAMS GREAT: I can stream 4K video files stored on the drive through the NAS just fine with network speed to spare. -- NOISY: The drives do make a lot of thumping noise that can be amplified by the table they sit on when the drives are active seeking, so if they are part of a home theater system as the case for me, you may want to think about installing them out of earshot if they are part of a NAS. I later added one to a Network Video Recorder and the 24/7 recording causes constant thumping sounds that can be very annoying. The NAS could be installed in another room but the NVR needs to be by the TV. I may replace it with another drive. -- PERFECT FIT: Mechanically the connectors and screw locations aligned perfectly in the NAS housing.Update: -- I bought a 3rd drive for use in in a Network Video Recorder for a home security system. It was instantly recognized and began recording immediately. Again it showed 3.6TB of available space but the thumping noise all the time is annoying.