The question (finally!)
Plug the new 2gb in the front usb slot?
Put Usb hub at back and plug both 2gb in?
Realise life is to short and go to the beach?
Ragnor: You probably don't want to use a usb hub as this would reduce throughput to the usb externals (2 drives sharing one lane), so if there is only 1 usb port on the back and 1 port on the front and two usb external drives I would use 1 on the front and 1 on the back.
The correct longer term solution would be to upgrade the capacity of the drives in the NAS:
1: Check the NAS model's page for supported hard drive make and size
2: Buy new hard drives (eg: WD Red's at 4TB's are about $250 each now, if your NAS can support them, and 2TB's have come down a lot too)
3: Follow the manufacturers guide to upgrading/switching hard drives for the model, usually it's replace 1 drive, wait for the raid array to rebuild then replace the other drive(s).
Is an English Man living in New Zealand. Not a writer, an Observer he says. Graham is a seasoned 'traveler" with his sometimes arrogant, but honest opinion on life. He loves the Internet!.