David Wright composed on 2025-08-18 11:13 (UTC-0700):
On Mon 18 Aug 2025 at 00:31:13 (-0700), Van Snyder wrote:
Is this an unavoidable intrinsic problem with UEFI, or is it a twelve-
year-old bug in grub-install or grub-mkconfig — or whatever the Debian
installer uses?
I don't think you've posted your new layout, so I'm only guessing.
It's not the size of the disk (<2TB), but you did have the EFI in a
logical partition, not a primary one. AFAIK that's not necessarily
out of specification, but it might not be supported by your
particular machine's firmware.
I'm coming up short finding the authority on this, but I'm pretty sure there is no
such thing as booting from an ESP that isn't on a GPT-partitioned disk, with
correct type assigned. I think the ESP type is technically at least a 4byte value
not supported by MBR disks, which are limited to 2byte types. The ESP also has a
unique UUID type c12a7328-f81f-11d2-ba4b-00a0c93ec93b that has no place in an MBR
table.
The boot record is MBR not GPT, but with the EFI partition primary and at a low enough address, the grub installation worked.
As far as I can tell, one cannot change the boot record to GPT without wiping out the partition table, which would require me to take a backup of the 1 TB drive.