Not advisable to do raid1 on giant disks like 4TB unless you are absolutely sure to turn it into an redundant array for data protection. Reason, our precious personal data hardly exceed 100GB. 4TB is overkill and once you setup, managing 4TB of data is a chore even with your super fast PC. Rebuilding of array is nice in theory when 1 disc fail, but rebuilding a 4TB array will probably takes more than 24 hours. You could be sitting in front of your pc for days when the 4TB hit the ceiling.
For redundancy raid1 setup, best is to do software raid1 with Linux OSes like ubuntu server using software raid.
Of course, you can setup the 4TB on your motherboard raid controllers, which is what normally called fake raid(using the hardware raid driver), however, should your motherboard failed in couple of years time due to usage for gaming and overclocking, you will have problem finding the same raid controller or motherboard to recover 4TB of data in your array. That's a big no no.
Alternatively, if you get a cheap nas like those dlink dns-320L. You are in better hands because, one, the nas are likely to survive longer than your motherboard and two, you are more likely to find an second hand nas to recover your data.
Whichever scenarios arises where you need to relocate or recover your raid1 array, moving 500GB is significantly less challenging than moving 4TB of data.
I'm a little like in your situation where my 4TB is in a nas. But I'm more inclined to free up 2x 500GB hard disk to put them as raid1 in my second nas,
Instead of getting a new 4TB into the first nas and had them setup in raid1.
So, consider your options above. I do have 2x 500GB in ubuntu software raid1. The reason software raid is preffered because, if the motherboard dies or I change pc, software raid aarray can be easily ported to the new pc as software raid is not hardware driver dependent.
It was noted, there is little difference in performance between software raid and fake raid(using motherboard controller). The real hardware raid requires one to buy expensive raid controller from the specialized suppliers, which has good chance of selling you a 5 years old at exorbitant price, but you have no choice because you have 4TB of data to recover 5 years later...
So weigh your situation where before committing a 4TB array. Money isn't the most critical but sitting in front of your pc for days trying to recover 4TB of data isn't a fun thing to do.
