On Fri, 24 Jun 2022 23:00:02 +0100
Wol [off-list ref] wrote:

So your boot device is currently in physical connector 1 on the mobo. If 
you move it across, you need to make sure it stays in physical position 
1, otherwise the mobo will try to boot off whatever disk is in position 
1, and there won't be a boot system to boot off!

Using RAID1 across all disks with metadata 0.90 for /boot makes sure the BIOS
can boot no matter which disk it tries first.

In fact it could be with recent grub the "0.90" part is not even required
anymore.

Just make sure to "grub-install /dev/sdX" at least once to all of them.

-- 
With respect,
Roman