When all else fails, I use a usb3 NIC until the correct NIC drivers are 
found :-)

I think you can use another disk to install UEFI setup and boot your 
raid from that install. If you do not have a spare disk, use USB to 
experiment. They are cheap to buy and use as you only need a bare 
install (on USB)  to get started.

I converted several legacy to UEFI. However, none was from a RAID. I 
always leave 32G in every install/boot disk for crunch work like this. I 
recommend this. Even the machine that has RAID1 boot has first 32G on 
each RAID1 disk unused (so that I can convert this install too into 
UEFI, when I decide to)

Note that you need GPT for UEFI boot disk. So, separate disk/USB is the 
best.

Ramesh


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

Thanks all,
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?).

Anyway, now looking for a network driver for this mobo...  ;-)

On 6/28/2022 2:57 PM, Ram Ramesh wrote:

quoted

On 6/28/22 16:32, Alexander Shenkin wrote:

quoted

On 6/27/2022 7:26 AM, Pascal Hambourg wrote:

quoted

On 27/06/2022 15:57, Alexander Shenkin wrote :

quoted

CSM is greyed out.  I think I need a graphics card

Is secure boot disabled? Legacy boot is not compatible with secure 
boot.

There's no way to completely disable secure boot on this mobo. It's 
an Asus Prime B560M-A.

Can you boot legacy install with UEFI boot disk? Have you  tried 
booting with sysrescuecd or some such to boot your installed OS?

Have you considered converting UEFI? CSM/Legacy boot support is 
dropping steadily. Sooner or later it will be extinct.

Regards
Ramesh