[Bug 2060695] Re: 24.04 grub-pc cannot upgrade on mirrored software RAID root disk

[Mate Kukri]

Can you provide a bit more detail about the exact disk layout being used
here?

Is the RAID on the bare disks, or are there partition tables containing
the RAID?

Also is there a partition table inside the raid, or is it directly
formatted as ext4?

Is LVM used anywhere?

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Title:
  24.04 grub-pc cannot upgrade on mirrored software RAID root disk

Status in grub2 package in Ubuntu:
  New

Bug description:
  I am testing the 24.04 pre-beta in a libvirt virtual machine with two
  /dev/vd* disks set up as a single mirrored software RAID device,
  /dev/md0, that is used for the root filesystem. Since this is a
  libvirt install, it is using BIOS booting, not UEFI (maybe someday
  libvirt will support snapshots of UEFI based VMs). When I attempt to
  install Ubuntu updates, the grub-pc install fails with:

  grub-pc: Running grub-install ...
  Installing for i386-pc platform.
  grub-install: warning: File system `ext2' doesn't support embedding.
  grub-install: warning: Embedding is not possible.  GRUB can only be installed in this setup by using blocklists.  However, blocklists are UNRELIABLE and their use is discouraged..
  grub-install: error: diskfilter writes are not supported.
    grub-install failure for /dev/md0
  You must correct your GRUB install devices before proceeding:

    DEBIAN_FRONTEND=dialog dpkg --configure grub-pc
    dpkg --configure -a
  dpkg: error processing package grub-pc (--configure):
   installed grub-pc package post-installation script subprocess returned error exit status 1

  'debconf-show' reports (changed) settings as:
  * grub-efi/cloud_style_installation: false
  * grub-pc/install_devices: /dev/disk/by-id/md-name-ubuntu-server:0
  * grub-pc/install_devices_empty: false

  The same mirrored root filesystem configuration works on 22.04 LTS.

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