I can't seem to get more than 7 units accepting shares with rasp pi +cgminer and a sabrent 13 port hub...always 7 units only anyone know solution
I hear people having success using a 10 port hub. But there are problems using over 10 ports. I'm using the cubieboard2 and two sabrent 13 port adapters with 25 gridseed. It can see all the devices. Try the below link for supported powered usb hubs. Good luck.
http://elinux.org/RPi_Powered_USB_Hubs