Thank you for the reply, good to at least get confirmation it should and does work.
Unfortunately, I am not in front of my test system at the moment. In a couple of hours I can give specific examples. So I am working on memory, so take it for what little this is worth.
If boot to a grub prompt and perform a “ls”, I see (hd0,gpt1) … (hd0,gpt5). So grub sees the partitions:
gpt1 = fat32
gpt2 = swap
gpt3 = ext4
gpt4 = ext4 - unused at the moment
gpt5 = btrfs with multiple subvolumes, maybe that is the issue?
If I place the kernel and initramfs in gpt1 or gpt3, it loads the kernel and boots. However, I have not yet been able to boot with the files in (hd0,gpt5):/boot
I have tried:
(hd0,gpt5)/boot/kernel.img rw root=/dev/sda5
initrd (hd0,gpt5)/boot/initramfs-linux.img
If I change the above to (hd0,gpt1) or (hd0,gpt3) it boots.
I have also tried set root=(hd0,gpt5) and insmod btrfs with part_gpt
So far, no joy with gpt5. I am hoping to be able to get rid of the need for an ext4 volume.