Re: RAID b/w GPT and NON GPT partition.
On Tuesday 30 June 2015 11:55:20 Pascal Hambourg wrote:
> 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.
And entirely admirable idea. But how do you go about updating the bios
to do that in several Billions of older motherboards?
Good question that. In fact I just did 4 wheezy based installs that
failed, on a drive bigger that that bios ever had dreams of when it was
born, a 500Gb, and the last good ide/atapi drive in my collection.
It took the first 3 failures before it hit me that by the time grub wrote
its stuff, last thing in the install, that it was so far into the drive
the bios couldn't find it, emitting an out of disk message at boot time.
So I yelled, and kicked and screamed bloody epithets at the installer
until I had it convinced that partition 1 was a 1Gb partition at the
beginning of the disk and was labeled /boot.
Problem solved, and a wheezy derivitive is now running nicely on a 384
meg equipt old HP Pavillion with an athlon at 1Ghz.
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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