I believe folk are running 4TB fine. But also some are finding that certain NVME drives don't work in it either. I'm not sure how an NVME drive would hold out on storage for CCTV? I've got a 2TB drive kicking about that was in an old gaming laptop so may chuck that in and transfer the Hikvision cameras to Protect.Spec sheet says its limited to 2TB drive, not sure if that is a hard limit though.