The older v3.x/v4.x single bay My Cloud units primarily used WD Red drives as far as has been reported in this subforum.
There are several YouTube videos one can search for that detail how to disassemble the single bay My Cloud enclosure to get at the internal SATA drive and remove it.
One may want to review the following thread to try and improve copy/performance speeds if one has not done so already.
What particular performance problem are you having?
If Twonky media server related then see the following thread if you haven’t done so already.
https://community.wd.com/t/faq-twonky-dlna-media-server-setup-use/95373
