Hi,
Nicolas George wrote:
> Interesting. Indeed, “table-length: 4” causes sfdisk to only write 3
> sectors at the beginning and 2 at the end. I checked it really does not
> write elsewhere.
> That makes it possible to use full-disk RAID on a UEFI boot drive. Very
> good news.
\o/
(Nearly as good as Stefan Monnier's crystal ball. And that without
understanding the dirty details which cause the need for a small partition
table.)
> More and more firmwares will only boot with GPT. I think I met
> only once a firmware that booted UEFI, 32 bits, with a MBR
The Debian installation and live ISOs have MBR partitions with only a
flimsy echo of GPT. There is a GPT header block and an entries array.
But it does not get announced by a Protective MBR. Rather they have two
partitions of which one is meant to be invisible to EFI ("Empty") and
one is advertised as EFI partition:
$ /sbin/fdisk -l debian-12.2.0-amd64-netinst.iso
...
Disklabel type: dos
...
Device Boot Start End Sectors Size Id Type
debian-12.2.0-amd64-netinst.iso1 * 0 1286143 1286144 628M 0 Empty
debian-12.2.0-amd64-netinst.iso2 4476 23451 18976 9.3M ef EFI (FAT-12
So any system which boots this ISO from USB stick does not rely on
the presence of a valid GPT.
(The only particular example of GPT addiction i know of are old versions
of OVMF, the EFI used by qemu, which wanted to see the GPT header block,
even without Protective MBR.)
This layout was invented by Matthew J. Garrett for Fedora and is still
the most bootable of all possible weird ways to present boot stuff for
legacy BIOS and EFI on USB stick in the same image. (There are mad legacy
BIOSes which hate EFI's demand for no MBR boot flag. Several distros
abandoned above layout in favor of plain MBR or plain GPT. The price
is that they have to leave behind some of the existing machines.)
> GPT
> ├─EFI
> └─RAID
> └─LVM (of course)
>
> Now, thanks to you, I know I can do:
>
> GPT
> ┊ RAID
> └───┤
> ├─EFI
> └─LVM
Ah. Now i understand how accidentially useful my technical nitpicking was.
(A consequence of me playing Dr. Pol with the arm in the ISO 9660 cow
up to my shoulder.)
Have a nice day :)
Thomas
