How to create RAID 1 most efficiently?

Question

Windows

Colleagues!
There is Windows 8.1 Professional installed on the SSD. For greater reliability, I want to create a RAID 1 array, for which I bought a second SSD of the same kind.
The motherboard is Asus M4N75TD, and as I understand it, you should not expect a normal implementation of RAID from it at the iron level.
Question: how to make a RAID 1 of two SSDs on an already installed Windows without losing any data?
I already know half of the question and got into "disk management", but the item "create a mirror volume" is inactive. What could be the problem?
Thank you.
UPD.:
"Add mirror" became active, but when you select an unformatted disk, it says "not enough disk space"

Answer 1

in Windows, you can not place the system partition on the storage spaces raid

Answer 2

I do not recommend a soft raid, besides, there is a high probability of getting a drawdown in speed. And in general, raids on SSDs do not always work stably (there was an article on Habré).
Buy a controller. Or do it on the mother (support is declared).

Answer 3

raid1 protects against the death of the drive, but does not protect information from corruption.