To stop wdmcserverd and wdphotodbmergerd the following commands should work. Note that when one reboots the My Cloud both services will start up again.
/etc/init.d/wdmcserverd stop
/etc/init.d/wdphotodbmergerd stop
The following thread discusses how to permanently disable those two services.
http://community.wd.com/t/how-to-permanently-disable-wdmcserverd-and-wdphotodbmergerd/135878
