[arch-general] Quick question about post-MBR gap?

mike cloaked mike.cloaked at gmail.com
Wed Jul 18 14:40:48 EDT 2012

I am planning a test install using the new arch-install-scripts via
the latest netinstall images from releng (from today's date).

I know that for a system where I blow away all previous disc
partitions and partition from scratch I can create a 2MiB partition
(using MBR and NOT GPT partitioning) before the first formatted
partition on the HD and install grub2 during the base install.
However can someone please tell me explicitly if, for a system with
only BIOS (no UEFI at all), and no GPT partitioning but just plain old
MBR partitioning - is the recommended 2MiB post-MBR gap still a
"requirement" for that specific situation for grub2 to work? I can't
find that as an explicit statement in any of the documentation that I
have read for installs/grub2/partitioning! i.e. does grub2 still need
to embed the core.img file in the post-MBR gap as the preferred and
dev recommended approach in this case?

The reason I would like to have that explicit answer is that if I want
to install arch on a machine which has a pre-existing NTFS partition,
and possibly host-protected partition as well for Windows recovery, at
the start of the drive, then if the 2MiB post-MBR gap is a requirement
(rather than a nicety) for grub2 with BIOS and MBR partitioning (but
no GPT partitioning or UEFI) then unless the drive is re-partitioned
and the NTFS partition reduced in size and moved out by 2MiB then
there could be problems? However doing that partition jinking about
might itself lead to a few issues!

I am going to do an install with new partitioning on an old laptop to
check that I can successfully use the new install system (without AIF)
and hopefully that will work, but I also have other machines with
existing and important (to me) Windows partitions that I would really
like to NOT corrupt when installing arch to the partitions on their

The other reason I am asking this question is that I also have
existing dual boot laptops with Windows XP and arch with BIOS and MBR
partitioning - and at some point it would presumably be sensible to
move from the existing grub to grub2 - and on these systems where I
have already checked that there is only a 64 sector post-MBR gap -
will this lead to problems if I change from grub to grub2 if I don't
change the partitions to have a 2MiB post-MBR gap?

Thanks for any help on this - I have been doing reading and trying to
prepare without looking an idiot and being a good arch admin, but
there is quite a lot to read and I still can't find the answer to the
explicit question above!

mike c

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