Seagate 4TB IronWolf NAS Internal Hard Drive, 3.5" SATA 6Gb/s

NAS-rated, and each reason matters inside a multi-bay box: rotational vibration sensors so neighbouring spindles do not shake it off track, error recovery timing that stops the array dropping it, and conventional recording so a rebuild finishes in reasonable time.

A desktop BarraCuda in the same bay lacks all three, which is the classic and expensive substitution. For a video recorder rather than a file server, the SkyHawk drives are the correct class.