"don't set up MDRAID array for ESP, just have the ESP mirrored on all disks. "
Isn't that the entire point of utilising MD RAID-1 in the first place?
I've done as you suggest in years gone by with either metadata v0.9 or v1.0 (not v1.1 or v1.2) where the metadata is not at the start of the block device and therefore does not confuse a non-MDRAID-aware firmware or other OS.
OK now I get what you mean. In that case, one can reboot and select the other non-broken disk and the system will boot, with some hiccups due to degraded array, but it will boot.
Isn't that the entire point of utilising MD RAID-1 in the first place?
I've done as you suggest in years gone by with either metadata v0.9 or v1.0 (not v1.1 or v1.2) where the metadata is not at the start of the block device and therefore does not confuse a non-MDRAID-aware firmware or other OS.