Linux: GRUB2 cannot recognize LVM logical volume with mixed GPT and MBR

Table of Contents

1 GRUB2 cannot recognize LVM logical volume with mixed GPT and MBR

For example, if there is a LVM logical volume with GPT LVM physical volume, appending MBR LVM physical volume to the LVM logical volume will make GRUB2 cannot recognize the LVM logical volume.

error: disk ‘lvmid/<snip>’ not found.Entering rescue mode…grub rescue>


2 Cause

This is because GPT module is built-in to GRUB2 and MBR module is not built-in. There is a case that MBR module is built-in and GPT is not built-in too.

The grub-install will look up LVM physical volume and install needed module. The grub-install will call grub-mkimage and grub-bios-setup internally.

$ sudo grub2-install -v /dev/vda<snip>grub2-install: info: grub-mkimage <snip>–compression ‘auto’ ‘ext2’ ‘part_gpt’ ‘lvm’ ‘biosdisk’.<snip>grub2-install: info: grub-bios-setup <snip> ‘/dev/vda’.<snip>

The grub-install is run automatically when Linux is installed and when GRUB2 is updated.

  • There is only GPT LVM physical volume when Linux is installed, the grub-install will install only GPT module.
  • After Linux is installed, you add MBR LVM physical volume to LVM logical volume.
  • After reboot, GRUB cannot recognize LVM logical volume because part_msdos is not built-in.

3 Solution

Specifying module to be built-in by default when running grub-install is the best way. But at least Debian cannot specify module.

There are three solutions. I think that (3) is easy.

  • (1) Make the same partition type LVM physical volume with the first LVM physical volume. But the partition type of first LVM physical volume depends on environment.
  • (2) Run grub-mkimage/grub-bios-setup and install GPT and MBR modules after Linux is installed. But you need to run grub-mkimage/grub-bios-setup for each GRUB2 update till GPT LVM physical volume and MBR LVM physical volume are added. And UUID of LVM depends on environment.
  • (3) Run grub-install when LVM physical volume is added.
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