Since I only have VMware Essentials license I can't seem to open a support ticket with them.
I haven't had a chance to remove the Spare Drive in the raid to try that approach yet.
I did find this KB about the vmfs heartbeat in ESXi 6.0, so I just gave this a try to disable it: Enabling or disabling VAAI ATS heartbeat (2113956)
We'll see what happens I guess....