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

Fri Aug 19 22:59:27 UTC 2016
James A. Peltier <jpeltier at sfu.ca>

----- Original Message -----
| 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
| troubleshooting.

Yes, it's a Dell R710XD

| >  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.

I suspect this is the case.  when attempting to run grub-install the system claims that the grub2-efi-modules packages aren't installed, so this may be an installer bug.

| 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.

We'll try this and get back to you soon.

James A. Peltier
IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 604-365-6432
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices
Twitter : @sfu_rcg
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