Re: [gentoo-user] Boot gentoo with GTP Disk label

[Paul Hartman <paul.hartman+gentoo@gmail.com>]

On Wed, May 12, 2010 at 4:47 PM, Mick <michaelkintzios@gmail.com> wrote:
> On Wednesday 12 May 2010 21:47:41 Paul Hartman wrote:
>> On Wed, May 12, 2010 at 3:00 PM, Mick <michaelkintzios@gmail.com> wrote:
>> > On Monday 10 May 2010 17:01:02 Paul Hartman wrote:
>> >> On Sat, May 8, 2010 at 9:16 AM, claude angéloz
>> >>
>> >> <claude.angeloz@bluewin.ch> wrote:
>> >> > Hello,
>> >> >
>> >> > I installed a gentoo on a very recent system  (efi support) . AT the
>> >> > reception of the laptop  it was a disk label msdos, with a boot
>> >> > partition w** installer ... I changed that against  a GPt disk label.
>> >> > I can install without problem the gentoo , but now it doenst boot.
>> >> >
>> >> > I read some docs about gpt,mbr,boot principles and tried some tools
>> >> >
>> >> > - install the grub2 masked package and grub-install.
>> >> >
>> >> > - a special partion bios_grub  as 1st bootable partition.
>> >> > but actually no succesful...
>> >> > but in the parted i did not see this "bios_grub" as  flag...
>> >> >
>> >> > I found some  tips from the web , but i guess that was only valid for
>> >> > a macintel system, not a normal pc  with a disk labeled gpt and an efi
>> >> > support.
>> >> >
>> >> > I know that it is not required  an  efi partiton to boot the os with
>> >> > pc/bios and gpt disk. Or is it false ?
>> >> >
>> >> > If anybody has an other idea. Or I must  abandon the gpt disk label ?
>> >> > Is there an equivalent refitr in OS x86  ?
>> >>
>> >> I'm using GPT partitions and with the grub-0.97-r9 in Gentoo it has
>> >> patches to boot from GPT disks. I just did normal grub install as
>> >> usual and everything seems to work. I'm not using the partition label,
>> >> though, but only "root (hd0,0)"
>> >
>> > Interesting.  Does grub install its bootloader into the MBR, or in a GPT
>> > boot partition?  I am not at all familiar with this new way of booting
>> > systems.
>>
>> I think basically GPT is a replacement for MBR, everything basically
>> works the same way otherwise. GPT has features like redunancy, removes
>> limits of MBR (no primary/logical designation anymore, no 2TB limit,
>> etc). I think it has a somewhat MBR-compatible layout in the first
>> sector so non-GPT-aware things can still partially recognize it.
>
> Am I right to assume that your 1st partition on the 1st disk is the GPT boot
> partition and therefore its 1st sector is what would on a conventional disk be
> the MBR?

From the standpoint of the fake MBR table, I think you are correct. To
non-GPT-aware utils it'll look like GPT is a partition of some type
but when using GPT-compatible things that is completely transparent.
Wikipedia has a good description of how it all works under the hood,
check out the LBA-0 section of the article here:
http://en.wikipedia.org/wiki/GUID_Partition_Table

From a normal user's perspective, creating the partitions and
installing grub was no different than with MBR, only I told parted to
great GPT instead of MBR partition table on my new disks. Enabled EFI
in kernel, used Gentoo's version of grub which has the GPT patches
included, and everything just worked. Maybe I was lucky? :)