Re: Problematic upgrade from 7.2 to 8.0 with ZFS file system

On Tue, Jul 14, 2009 at 8:29 PM, Aristedes Maniatis<ari_at_ish.com.au> wrote:
> Last night we upgraded one of our servers from 7.2 to 8.0-beta1 using the
> freebsd-update tool and following the instructions on Colin's blog. I
> believe this problem will occur even if we had used a source update
> mechanism.
>
> The usual upgrade path is to install the new kernel, reboot, then install
> world. This fails because when rebooting into the 8.0 kernel with 7.2
> userland, ZFS is unable to properly initialise and the file systems are not
> mounted. In our case we are booting with a small UFS partition to load the
> kernel, and then mounting /usr /var, etc from ZFS as per these instructions
> [1].
>
> The problem with ZFS userland being out of sync with the kernel has been
> seen before [2] [3]. However now with lots of people running ZFS and
> starting to upgrade to 8.0, I think this will bite many more.
>
> The workaround is to drop into single user mode, mount all the zfs
> partitions, and do the userland install.
>
> mount -t zfs /usr
> mount -t zfs /var
> mount -o rw tank/root /
>
> Those mount commands are slightly non-obvious and took a little guessing to
> get right. You can't use the 'zfs mount' command since it is broken at this
> point in time.
>
> The other solution is to install userland BEFORE you reboot into the new
> kernel, although that may cause its own set of problems. Whatever the final
> solution, this needs to be clearly documented and ideally freebsd-update
> needs to detect the problem and advise the user about what to do.



Do to the large version jump (v6 -> v13) the kernel interfaces aren't
backward compatible with the tools. How do you think it could be most
gracefully handled?


 -Kip