I will be building a NAS with the x86, too. It will also carry one USB 4TB Drive. What you have to keep in mind though is that USB, depending on the USB chipset in the drive, lacks proper smart support and can cause trouble if you use any kind of raid (slower mounting at boot for example can cause such issues).
This post is just to inform you that I have edited the title of the topic since there is no specific problem of the SATA of UDOO X86 at the center of this discussion.
