ZFS failed after hard power off

[Artem Belevich]

On Thu, Mar 31, 2011 at 9:48 AM, Piotr Paczynski <ppaczyn at gmail.com> wrote:
> Hi all,
>
> I urgently need help. After hard power-off (power cable disconnected)
> my FreeBSD 8.1-STABLE server fails to boot from ZFS with an I/O Error.
> I was able to boot to Fixit console from 8.2 LiveFS, prepare it for
> ZFS and mount the pool using "zpool import -Ff" command. Here are the
> results:
>
> Fixit# zpool status
>   pool: zroot
>  state: FAULTED
> status: The pool metadata is corrupted and the pool cannot be opened.
> action: Destroy and re-create the pool from a backup source.
>    see: http://www.sun.com/msg/ZFS-8000-72
>  scrub: none requested
> config:
>         NAME         STATE   READ WRITE CKSUM
>         zroot        FAULTED    0     0     1 corrupted data
>           gpt/array0 ONLINE     0     0     6
>
> Also "zdb -l /dev/gpt/array0" shows 4 LABELS. Each has the same
> attributes, in particular:
>   version=14
>   state=0
>   txg=4
>

Something like this could've happened if the drive lied about having
data committed to platters. If power fails, you may end up with
partially written data and inconsistent on-disk ZFS state.
You may need to boot into FreeBSD-9 with ZFS v28 or with OpenSolaris
live CD and re-import the pool with  "zpool import -F".

http://solori.wordpress.com/2010/07/15/zfs-pool-import-fails-after-power-outage/

--Artem