Assemble VMs from backup and more recent disks after GRUB failure on upgrade from 8 to 9

[Harald Oehlmann]

Tonight was a quick update of Proxmox 8 to 9 in release channel with outdated backups of Windows 11 and Linux VMs.
After the update, grub reseted the machine directly after the inverse "GRUB" printout.
Tried to make running with

• proxmox installation USB stick: did not find boot
• supergrub, Debian rescue, grml: did not find boot
• systemrescue with ZFS: was able to boot with "findgrub" profile. Different kernel booted, which had no modules. ZFS was solved by copying "modules" folder from systemrescue to proxmox, but KVM kernel module was missing, which did not allow a backup.

In consequence, Proxmox 9 was installed from scratch on system, but on differen USB hard drive.

• The present lvm volumes were renamed to include text "--OLD--" by the installer. They were activated by command line commands.
• The outdated backups were restored.
• The current disks were copyied by "dd if=/dev/pve...--OLD.../pce-01-disk-1 of=/dev/pve/pce-01-disk-0. Instresting was, that the disks were changed in order, e.g. disk 0 got 1 etc, wich is detected by the size.
• The system is rebooted
• VMs worked well

Thanks for great Proxmox,
Harald