[PVE-User] zfs root after last update grub unknown filesystem

[Arjen]

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, September 14, 2020 9:07 AM, Aaron Lauterer <a.lauterer at proxmox.com> wrote:

> Alternatively you can try to install the machine in UEFI mode. In UEFI mode with root ZFS the installer will set up systemd-boot instead of grub. This alleviates the problem with grubs limited ZFS compatibility.
>
> See the docs for more infos: https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysboot
>
> HTH,
> Aaron

I had the same problem with a zpool feature that could not be turned off. I used this work-around for a while in the hope that the bug would be fixed (GRUB patch existed for 5 years but it was never tested/reviewed):
Put a new Proxmox VE installation on USB and copy /boot from the hard drives to the USB installation.
With that, it could boot from USB, after which it would pickup on the rpool on the hard drives (probably by lucky chance).
Eventually, reinstalling with UEFI+GPT+ESP+systemd-boot (which did not exists when I encountered the issue) fixed it.

I would suggest taking the pain now, and reinstall using UEFI, to prevent such issues in the future.

> On 9/14/20 12:16 AM, Gianni Milo wrote:
>
> > GRUB does not support all zfs features, so it's quite common for it to fail
> > to recognise the rpool during boot if it has a feature which is
> > incompatible with it. In your case, I believe that is the "encyption"
> > feature.
> > Do you recall the issue starting after enabling encryption on rpool/data
> > dataset? If so, you may have to rebuild the pool and leave rpool/data
> > unencrypted.
> > Note that even though you enabled encryption only on rpool/data, the
> > feature will take effect at the pool level, hence the GRUB issue you
> > are facing.
> > Because of this issue, people have started using a separate boot pool
> > (bpool), with limited zfs features enabled and a different data pool
> > (rpool) for the OS and the data. I believe that the PVE installer should be
> > modified to follow this approach (if it hasn't done it already) to overcome
> > similar issues.
> > Gianni
> > On Sun, 13 Sep 2020 at 22:29, Stephan Leemburg sleemburg at it-functions.nl
> > wrote:
> >
> > > Hi All,
> > > I have a proxmox system at netcup that was clean installed about two
> > > weeks ago.
> > > It is full zfs, so root on zfs. I am migrating from one netcup system
> > > with less storage to this system.
> > > This system is using the pve-no-subscription repository, but after
> > > migration I will move the subscription from the 'old' system to this
> > > system.
> > > The rpool/data dataset is zfs encrypted.
> > > Today I did zfs send/recv from the 'old' system to this system to the
> > > rpool/data dataset.
> > > After that I did an apt update and noticed there where updates available.
> > > After the upgrade and the mandatory reboot, the system does not come up
> > > anymore. It is stuck in grub rescue.
> > > Grub mentions that it has a 'unknown filesystem'.
> > > Has anyone else experienced this same situation?
> > > If so and you could recover, what was the reason and fix?
> > > I am still researching what is causing this. If I boot a .iso then I can
> > > import the pool and see all datasets and subvolumes.
> > > So, it seems that the zpool itself and the datasets are ok, it is just
> > > that grub is unable to recognize them for some reason.
> > > I have read about other situations like this where large_dnode seemed to
> > > be the cause. I noticed that on the zpool large_dnode is enabled. And it
> > > is a creation only setting. It cannot be changed to disabled afterwards.
> > > This must have been done by the Proxmox installer. As booting is about
> > > the root filesystem, I guess the zfs send / recv to the rpool/data
> > > dataset would have nothing to do with it, but I could be wrong.
> > > I will continue my research tomorrow evening after some other
> > > obligations, but if anyone has an idea, please share it. If it is just
> > > how to get more debugging info out of the zfs module in grub.
> > > Because 'unknown filesystem', with the zfs module loaded is kind of not
> > > helping enough..
> > > Best regards,
> > > Stephan
> > >
> > > pve-user mailing list
> > > pve-user at lists.proxmox.com
> > > https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-user
> >
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>
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