[CentOS] GRUB 2 dumps to grub prompt when installed on >4TB disk

Thu Aug 18 23:08:07 UTC 2016
Chris Murphy <lists at colorremedies.com>

On Thu, Aug 18, 2016 at 11:57 AM, James A. Peltier <jpeltier at sfu.ca> wrote:
> Hi All,
> I have a Dell R710 that has 6x1TB in a RAID-5 configuration.

This is hardware RAID 5? Because it's pretty screwy how this ends up
working when using software RAID and might take additional

>  When installing CentOS 7 using the full disk capacity and booting in UEFI mode the machine dumps me into a GRUB rescue mode prompt.
>   error: disk `,gpt2' not found
>   Entering rescue mode...
>   grub rescue>

This is confusing to me because there should be no such thing as grub
rescue on UEFI. On BIOS systems, there is boot.img (formerly stage 1)
and core.img in the MBR gap or on BIOS Boot if GPT disk (formerly
stage 1.5 and stage 2). The core.img is where grub rescue comes from
when it can't find grub modules, in particular normal.mod.

But on UEFI, core.img, normal.mod, and a pile of other modules are all
baked into the grubx64.efi file founds on the EFI system partition.

I suspect two things that can cause normal.mod to not be found:
a. The system is not in fact booting in UEFI mode and there's been
some mistake in the installation of grub.
b. The system is in UEFI mode, but either the installer, or
post-install, grub2-install was run which obliterates the grub2-efi
package installed grubx64.efi, i.e. it's not really proper to run
grub2-install on UEFI systems.

Boot off install media with boot parameter inst.rescue and choose all
the default options; this ought to assemble the file system per fstab,
and you can

chroot /mnt/sysimage
yum reinstall grub2-efi
efibootmgr -v
grep efibootmgr /var/log/anaconda/program.log   ## I think that's
right it might be anaconda.program.log though

It's really just reinstalling grub2-efi that should fix the problem,
the following two options are just information gathering in case the
reboot still doesn't work.

Chris Murphy