How to mount exist already RAID?

I found this:
https://serverfault.com/questi…are-raid-to-a-new-machine
it is a general solution

After a fresh install my RAID1 was detected automatically.
I think this is the standard behaviour. But does not work always. In those cases some action from CLI is needed.

In any case: make sure to have a solid backup strategy.
https://www.backblaze.com/blog/the-3-2-1-backup-strategy/