I have a Asus Sabertooth 990FX Motherboard. Basically want to create raid with 2 SSDs. The SSD's I have got is Samsung SSD 840 Pro 512gb and the other 256gb. I create the raid 0, but when I press crt + f, and make the raid 0 the size of the drives is 509.99gb. how comes it doesnt use the full capacity?