[PVE-User] grub-install error: unknown filesystem, won't boot anymore

[arjenvanweelden at gmail.com]

Apologies for replying to myself.

On Fri, 2019-03-08 at 11:12 +0100, arjenvanweelden at gmail.com wrote:
> Dear readers,
> 
> My up-to-date (no-subscription) Proxmox installation at home stopped
> booting properly. GRUB complains at boot about:
>   error: no such device: <hex string>.
>   error: unknown filesystem.
> 
> I got my system booting again using a new installation of Proxmox on
> a USB-stick, because Rescue Boot option of the installation ISO did
> not
> work for me. Fortunately, my 4-way mirror rpool is just fine (as are
> the other ZFS pools), but grub-install, grub-probe, and insmod normal
> at GRUB prompt keep returning "error: unknown filesystem".
> 
> Last thing I did to my rpool was 'zfs set dnodesize=auto rpool' as
> suggested on the ZFS Tips and Tricks official Wiki-page.
> Reverting to dnodesize=legacy did not fix the GRUB boot issue.
> 
zpool get all rpool shows:
  rpool  feature at large_dnode  active  local

I guess this make me run into a GRUB bug?
  https://savannah.gnu.org/bugs/?func=detailitem&item_id=48885
If so, suggesting 'dnodesize=auto' on the Proxmox Wiki might not be the
best idea until the bootloader used by Proxmox supports it?

> Currently, my system is booting partially from the USB-stick and
> partially from my original rpool, which works but is not ideal.
> Does someone recognize this problem? Does anyone know a fix?
> 
Is there a way to disable/undo large_dnode?

kind regards, Arjen