A:Answer Only the WD RED PRO drives are base 7200 RPM. The My Book Duo does not use WD RED PRO drives, just WD RED. These drives use WD's "IntelliPower" RPM rating, which is base 5400 but they say can operate in the range of 5400-7200.
http://www.pcmag.com/article2/0,2817,2407614,00.asp