Software RAID 1 is better than hardware RAID 1! Here's why:
1. Hardware RAID controllers do fail, and when they do, they kill all hard drives connected to them.
2. If your controller didn't fry your hard drives when it failed, you'll have to find the exact replacement, or you can kiss your data goodbye. You installed a hardware RAID array using second hand Broadcom controller three years ago, and now it failed? You better get on looking for the same controller of same revision running the same firmware version (of course you can't update firmware yourself) if you want your data back. Oh, Broadcom discontinued this model? Tough cookies. With software RAID, everything is easily recoverable.
3. You save a lot of money you can invest in other parts of your system. Good hardware controllers, even second hand ones, don't cost less than $200.

Performance loss is negligible.
RAID built into your motherboard is the worst of both worlds: it's just the software RAID you can't reallly control. Don't do that.

Hardware RAID is only worth it if you have a contract with your hardware supplier that says they're responsible for managing your RAID array. They have the resources to replace failed controllers properly. You know how IBM installs full rack worth of servers just to disable 70% of them because of your plan limitations? It's easier for them to do that than to physically go there and take servers away, just to reinstall them when you grow. Yeah, that kind of contract at that kind of level. If you're there, you don't need me telling you all that.

TL;DR: if you want to buy a two 8TB hard drives for $150 each on newegg and a used RAID controller to make RAID 1 array, you can make both 16TB _and_ make your system more reliable. Reliability is what you're after if you want RAID 1, isn't it?

What are you do... wha... no! stop! are you gonna buy a raid box from Aliexpress? are you fucking crazy?!