On 29/06/2022 04:10, Ram Ramesh wrote :

Note that you need GPT for UEFI boot disk.

This is only a requirement for Windows (and possibly broken UEFI 
implementations). The UEFI specification allows to boot from a drive 
with a DOS/MBR partition table. Else, assigning a DOS/MBR partition type 
code for EFI system partition (0xef) would be pointless.

On 6/28/22 20:05, Alexander Shenkin wrote:

quoted

Once I installed a graphics card, I was able to enable CSM and I've 
booted successfully.  Thanks everyone for your help. Converting to 
UEFI would be a good idea, though not sure how easy that will be given 
that /boot is a RAID1 array (how do you resize all the partitions, etc?).

Setting up redundant EFI boot with software RAID is a pain and a hack.
Resizing RAID partitions is a pain.
So I advise you keep legacy boot as long as you can (but prepare for EFI 
boot on a test machine or VM).