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

[Aaron Lauterer]

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

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
>>
>>
>>
>>
>>
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>>
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>>
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>>
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>>
>>
>>
>>
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