Can someone help me understand RAID-assistant?

[kladda]

Hi! I would like to get some help understanding the Sierra RAID functionality.

I have tried setting up a software RAID 1 and i works fine. Altho i h ave some questions:

1. In the setup i can choose that is should automatically rebuild. I copy some text from MacWorld. "If you are building a RAID 1, you’ll see an option to “Automatically rebuild.” This means that if a drive is removed and then replaced, the data will automatically be restored to the new drive. Check this box if you want this option. If you don’t, you rebuild the RAID using the Disk Utility app." When is this going to be in use (and how will i be notified about it)? How does the RAID know that a new disk i connect should be part of the RAID?
   
   
2. Also, there is a new Repair button. What does this do? For example if a disk has crashed, what is the differens between hitting Repair and just adding a new disk and letting that new one rebuild from the one that did not crash? Is the repair some kind of software repair to fix a broken disk, and if so, why is it asking me what disk i would like to add? (I do understand it can't fix a physicall errors )
   
   
3. If one of The disks in a raid 1 fails, Will i get any kind of alert of massage? Googled this any everyone said "nope", but that was on OS X 10.6, 10.8 etc. What about now, do we get a alert or is there any modern software that can help me with this?

Would love to get some help here

Thanks!