Received this from WD support. This is so lame that I can hardly fathom it. Sierra has been out since September and they see to be simply writing off all of those customers. Unbelievable. Why should I ever buy a WD drive again?
"Thank you for contacting Western Digital Customer Service and Support. My name is …
I have read your description carefully. I would like to ask you if you have ever used that device with Sierra. Because as you can see in page 2 Sierra is not compatible:
User Manual (PDF)
Sierra is much more recent OS in regard with the MyBook and so it is not tested if works properly.
If you have any further questions, please reply to this email and we will be happy to assist you further."