[Ukfreebsd] Confused by ZFS root(s)

[Jon Schneider]

Morning all,

I am currently gaining control of 11.0 servers left behind by somebody 
else and the first things to do are password reset, health check, backup 
and snapshot.

I am a ZFS newby but it's growing on me. One thing confusing me is the 
weird filesystem root arrangement.

NAME                 USED  AVAIL  REFER  MOUNTPOINT
zroot                214G   685G   144K  none
zroot/ROOT          96.7G   685G   144K  none
zroot/ROOT/default  96.7G   685G  96.7G  /

On this particular server I booted off a stick, did

zpool import -fR zroot somewhere
then
chroot somewhere passwd
then
zpool export zroot

and that was fine.

I then set up a Virtualbox machine for a colleague to train on with a 
memstick image and a couple of blank disks. I installed with the "Guided 
ZFS root" option. I then tried the same break-in procedure but after 
zpool import the guts of the system just wasn't mounted. I just had the 
other filesystems (various usr and var).

I had to

zfs mount zroot/ROOT/default

then proceed as before.

So 1) What are these extra (filesystem) roots about apart from confusing 
me ?
2) Why might my virtual machine not mount the important one 
zoot/ROOT/default ?

Jon