RAID 1 replacement of the first disk?

Question

Debian

I bought an old Supermicro server for all sorts of experiments and other things, I’ll say right away I’m just starting to get comfortable with Linux, by trial (tambourine) and googling I installed it in RAID 1 (if I’m not mistaken, I set ANCI instead of RAID in the BIOS and created a raid array in the Debian installer menu , I also tried iron RAID earlier 1) Debian, the essence of the issue is - I take out the second disk - the system boots, I take out the first disk and nothing - only the cursor blinks, I tried to put the second disk instead of the first disk - everything is the same, parallel to Google and read the info, Google prompts that it's in GRUB, but something doesn't quite work out, I'll be glad if someone in the topic shares their knowledge.
PS when I tried an iron raid - the removal of the second disk showed the regraded status and the system started, but if the first disk is removed, the status is failed, only the cursor blinks, the toaster has an answer very similar to my question, but not everything is clear

Answer 1

So, what is the software raid based on?
If it is made on Linux, then Linux needs to boot first, and only then enable the raid, so either your boot is not in the raid, and therefore only on one of the screws, or some magic