[gentoo-user] Re: MBR & GPT dual compliant format

[James]

R0b0t1 <r030t1 <at> gmail.com> writes:

> On Jul 22, 2016 5:43 PM, "Neil Bothwick" <neil <at> digimed.co.uk> wrote:
> > I take it this is a limitation of Apple's firmware as I have set up a
> > number of uUEFI systems and never had to do this.

> It is.


There is another document that talks in depth about the issue, although
it was centric to using gpt disk on a bios world that was slowly moving
to efi [1].


[1] http://mjg59.dreamwidth.org/8035.html

Here is the essence::
"But most BIOSes (and most older operating systems) don't understand GPT, so
plugging in a GPT-partitioned disk would result in the system believing that
the drive was uninitialised. This is avoided by specifying a protective MBR.
This is a valid MBR partition table with a single partition covering the
entire disk (or the first 2.2TB of the disk if it's larger than that) and
the partition type set to 0xee ("GPT Protective"). GPT-unaware BIOSes and
operating systems will see a partition they don't understand and simply
ignore it."


I do not know how to set up a 'protective MBR', that's my issue. This
reference goes on to talk about how the code was written for parted but
never made the permanent status. It sure would fix a lot of installation
issues among many different distros. An excellent read, if anyone has the
time. Me, I'm going to use this method::

1. First, write an example of what the partition table should look like.

2. Figure out the separate tools & sequences to achieve the final result.

3. Document the steps so they are clearly available for our community.

4. Hope that one of the devs/hackers spins a patched version of a "parted"
formatting tool to achieve this ability, system-rescue seems  to be the best
home. Or if a patched parted only lives in an overlay, that would ease quite
a lot of pain for many folks as in my research experience, setting up the
disk partitioning schemes is the toughest part of an installation these
days. This duality of disk usage  is critical to my cluster testing schema.
I'll  also have a variety of bootstap codes to deal with from various
embedded systems, in addition to commonly purchased hardware platforms, so
extending the formatting to other forms of storage, in a consistent and
generic way, provides an even greater appeal.

From the same doc::
"It violates the spec and it confuses the majority of partitioning tools. I
wrote some code to make parted do it at one point, but I don't believe it
was ever merged. It's very difficult to make it work well. "

They discuss also some of the MAC family of issues and explain why macs
still suffer from this malaise. I hope that code is still around....


Thanks for all the advice and help.
James