Add a new disk as mirroring (raid 1) to existing disk

Yes, you are correct.

There are inumerable internet guides available on how to do this. As several steps are involved, Windows RAID guides may give the impression this is a somewhat complicated process. It is not.

The Windows Disk Manager guides the process making it very easy to add a RAID configuration and rebuild a failed set. Therefore my suggestion is to get your hands dirty on a test system first and follow up by more in-depth reading about RAID therory and practice afterwards.

What is not covered as often in the internet guides is when a mirrored boot disk fails and how to replace the failed member in such a set. It was quite a while since I had to do this using Windows software RAID and I cannot remember exactly what had to be done. But if the ”wrong” disk failed I faintly recall a text file having to be updated with the remaining member guid, or something of the sort. And possibly this fossilized NT4-age artefact has now been replaced with a more helpful mechanism in more recent versions of the OS...

Maybe try your hands with a virtual machine using VMware workstation, VirtualBox or other VM manager? It makes adding and removing different disks easy and with a VM snapshot you can easily reset the whole system if you get yourself cornered. Just to start practicing and building the disk management skillset before going bare metal if that is your goal.

A final caveat: sometimes a new RAID practicioner will confuse RAID with backup. They are not the same and cannot be replacements for each other.

RAID lessens the risk of a system or data availability failure by adding redundant online copies of data. If data is corrupted or deleted, it is not recoverable through RAID even though the system may still be functioning in other respects thanks to RAID.

A backup safeguards data by storing offline copies of it. If the online data is lost or corrupted it can therefore be restored.

Critical systems usually have both RAID and backups for this reason.