Re: RAID b/w GPT and NON GPT partition.
Christian Seiler a écrit :
>
> So if you want to boot from GPT partitions, you need to have a
> small-ish (I typically use 100-200 MB or so) FAT32 partition of
> the "BIOS Boot Partition" type at the beginning of the drive.
> That's where the boot loader will be installed. (And you need
> EFI to boot that.)
You are confusing the "BIOS boot partition" with the "EFI system
partition" needed to boot from UEFI firmware in native mode.
The "BIOS boot partition" can be as small as ~50 kB or even less (it
replaces the MBR gap which used to be 32 KiB) and is used by grub-pc to
boot from BIOS (or UEFI in legacy/CSM mode).
Even the EFI system partition does not need to be that big for Debian.
The bootloader size installed by grub-efi-amd64 is less than 1 MB.
Also, there is no strict requirement that the EFI system partition must
be at the beginning of the disk. This is just a precaution against
possibly broken UEFI firmwares.
> The reason why GRUB can't be installed traditionally is that
> on MBR-style hard drives it uses the empty space of cylinder 0
> (typical a couple of MB)> after the boot sector (but before
> cylinder 1, which is the first cylinder that may be used for a
> partition)
Err no. The first partition used to begin at head 1 (LBA sector 63, i.e.
32 KiB), not cylinder 1 (LBA sector 63 * number of heads). Since virtual
CHS geometry has been deprecated and "Advanced Format 512e" hard disks
and SSDs have been around for a while, partitions are aligned on 1 MiB
boundaries, so the first partitions starts at 1 MiB, i.e. LBA 2048.
> to put in the executable code that can read the
> filesystem of the boot partition. Unfortunately, GPT uses that
> space itself, so GRUB can't go there.
Actually GPT does not use *all* that space and GRUB could still find out
the available unused space. But the GPT partition table could grow and
overwrite the beginning of the bootloader, so I guess it was considered
safer and cleaner to create a dedicated partition type. I agree with
this point of view and wish such a type also existed for MBR partition
style.
Reply to: