ZFS: unsupported ZFS version 5000 (should be 28)

[Tim Gustafson]

I recently rebuilt my FreeBSD 8.4 OS and rebooted, and when the system
came back up, it refused to mount the zpool because:

ZFS: unsupported ZFS version 5000 (should be 28)

I didn't upgrade my zpool as far as I know.  I tried booting off the
latest 9.1 snapshot, but it also says that the zpool has a too-new
version number and won't import it.

I Google around and found a post about using gpart to update the boot
code, which I tried with both the newest 8.4 release and also the
newest 9.1 snapshot, just to make sure something wonky didn't happen
with the disks.

The good news is that I have relatively recent backups (yesterday
evening) for this system, but I'm still totally confused as to what
the heck happened.

Is there some magic that I can type into a live boot CD to fix this
problem without rebuilding the whole machine?

-- 

Tim Gustafson
tjg at ucsc.edu
831-459-5354
Baskin Engineering, Room 313A