As explained in another recent thread (link below) I am usually able to get at least five devices recognized and mount by the My Cloud using an old Belkin 7 port USB hub. Further in that thread I show that it is possible to have seven items detected but I had problems with the seventh device where it wouldn’t say mounted for more than a few seconds. My speculation in that thread was possibly power draw of the other devices was causing the seventh device to intermittently mount.
http://community.wd.com/t/my-cloud-and-usb-hub-powered/168885/2
Chances are there will be no definitive list because of the wide variety of USB hard drives and flash drives there are out there and the fact that in certain cases those devices may draw more (or less) power than the USB specifications call for and USB hubs may put out more or less power (per port) than the USB specifications call for. What USB hub works for one person may not work for another.
