Getting ZFS pools back.

[Warner Losh]

On Sun, Apr 29, 2018 at 12:31 PM, Jan Knepper <jan at digitaldaemon.com> wrote:

> However, most 11.x binaries work well enough to at least bootstrap / fix
> problems if booted on a 10.x kernel due to targeted forward compatibility.
> You shouldn't count on it for long, but it generally won't totally brick
> your box. In the past, and I believe this is still true, they work well
> enough to compile and install a new kernel after pulling sources. The 10.x
> -> 11.x syscall changes are such that you should be fine. At least if you
> are on UFS.
>
> However, the ZFS ioctls and such are in the bag of 'don't specifically
> guarantee and also they change a lot' so that may be why you can't mount
> ZFS by UUID. I've not checked to see if there's specifically an issue here
> or not. The ZFS ABI is somewhat more fragile than other parts of the
> system, so you may have issues here.
>
> If all else fails, you may be able to PXE boot an 11 kernel, or boot off a
> USB memstick image to install a kernel.
>
> Generally, while we don't guarantee forward compatibility (running newer
> binaries on older kernels), we've generally built enough forward compat so
> that things work well enough to complete the upgrade. That's why you
> haven't hit an issue in 18 years of upgrading. However, the velocity of
> syscall additions has increased, and we've gone from fairly stable (stale?)
> ABIs for UFS to a more dynamic one for ZFS where backwards compat is a bit
> of a crap shoot and forward compat isn't really there at all. That's likely
> why you've hit a speed bump here.
>
> I have not closely looked at the procedures outlined in /usr/src/UPDATING
> for 11.x. But do I read correctly that performing a buildworld,
> buildkernel, then installworld and reboot to update from 10.4 to 11.x does
> not work?
>

No. That will work. If you always install a new kernel and reboot
(especially across major releases) and then install the new binaries,
you're safe. You won't get into a situation where new binaries are running
on an old kernel. As far as I know that's not broken, even with the strange
ABI issues I talk about. That's only when you're running 11.x binaries on a
10.x kernel, not the other way around.

Warner