https://www.hardware-journal.de/testberich... - How could it be otherwise, WD uses its own Red series. In this case, two of the 4TB models (WD40EFRX). These hard drives come with 64MB cache and are operated with a maximum rotational speed of 5400 rpm. The manufacturer specifies an operating volume of 28dB(A) (operation) and 25dB(A) (idle). Exact volume measurements / assessments were also recorded and documented by us. The results can be found in the volume measurement.