zpool won't mount as dataset stuck

[Geoff Roberts]

Hi,

In a slight panic here as my main ZFS pool "tank" won't mount.

I have two ZFS pools on two different drives - a system pool on a  
single disk called "data" and a mirrored pool on two disks called  
"tank".

The "tank" zpool contains all my jails and non-system boot type data.

I was wanting to test FreeBSD 8.2-PRERELEASE and therefore took a  
snapshot of "data" and "tank":

zfs snapshot -r data at pre82
zfs snapshot -r tank at pre82

"tank" seemed to hang on the above command for ages and I had to Ctrl-C.

Long and short is I can see the "tank" zpool without a problem, but  
whenever I try to import it the disk light flashes every second and  
the datasets won't mount.

I can run a history command on "tank" and that shows the following  
repeated every second (tgx keeps incrementing by one):

2010-11-28.15:08:33 [internal rollback txg:9645688] dataset = 222  
[user root on systemname.com]
2010-11-28.15:08:34 [internal rollback txg:9645689] dataset = 222  
[user root on systemname.com]


The zpool seems to be stuck.

What should I do from here?

Is there a way to "freeze" dataset operations so I can at least mount them?

Other thoughts and questions I had:

a) What would be the best way to take a raw image of the zpool so I  
can work on a copy of the zpool rather than the original?

b) Would it be worth trying to import the zpool on FreeBSD current or  
OpenSolaris?

Any help greatly appreciated.

Kind regards,

Geoff