ZFS fails with error 6 on upgrade to 11.1

[Sebastian Schwarz]

Hello,

With 11.1 just officially announced I decided to give it a try
on my notebook.

After creating a boot environment I upgraded from
11.0-RELEASE-p11 to 11.1-RELEASE-p0 following the instructions
outlined in
https://www.freebsd.org/releases/11.1R/installation.html:

# freebsd-update fetch install
# freebsd-update -r 11.1-RELEASE upgrade
[manually merge /etc/mail/mailer.conf]
[manually merge /etc/syslog.conf]
# freebsd-update install
# shutdown -r now

At this point the boot process errored out with the following
error message:

> Mounting from zfs:ssd/ROOT/freebsd11.1.0 failed with error 6.

The following prompt lets me list all available devices.  All
the drives for the ZFS pools are present with the same names as
in `zpool status`.

After that I rebooted and selected the previously created boot
environment with 11.0p11 and am trying to figure out the
problem.  However as I'm fairly new to FreeBSD I'm in need of
some help.

Some background information on my setup:

- booted with EFI
- the drives are partitioned with GPT
- the two ZFS pools where originally created on Arch Linux
- from the FreeBSD installer I successfully installed into a
  separate dataset
- 11.0 has been working fine like this since December 2016

More details:

- dmesg: http://ix.io/yHR
- gpart list: http://ix.io/yHT
- zpool status: http://ix.io/yHZ
- zfs list: http://ix.io/yHQ

Some advice would be very much appreciated.

Thanks in advance,
Sebastian