The issue of the My Cloud being slow on the Mac has been commented on from time to time. Might want to do a subforum search (magnifying glass icon upper right) and read the previous threads to see if there is any real solution. For starters may want to see how the Mac is connecting to the My Cloud, is it AFP or SMB or some other method. One may want to “map” the My Cloud to the Mac which may speed up the initial access some what.
Here are a few prior threads:
http://community.wd.com/t/support-os-x-el-capitan/96744
http://community.wd.com/t/wdmycloud-is-slower-with-mac-os-x/95800
http://community.wd.com/t/mycloud-very-slow-on-mac-after-fw-update/92596
http://community.wd.com/t/painfully-slow-transfer-speed-mac-gig-ethernet-wd-mycloud-4t/92523
http://community.wd.com/t/wd-mycloud-mac-problems-and-slow/94880
http://community.wd.com/t/smb-on-mac-is-impossibly-slow-in-reading-a-large-directory/148857
