Can't mountroot from ZFS pool

[Steve Bertrand]

All,

I've successfully upgraded the disks in my ZFS backup server, and can
import/mount the pool properly.

However, I designed this box originally so that it mounts / from
zfs:storage after booting from a USB stick.

After the upgrade of the disks, I'm stuck at a mountroot prompt when I
attempt to boot the system with the original USB /boot key.

Can someone inform me how to find the / filesystem at the mountroot
prompt? If not, is there *any* way to boot the system normally from
another medium, and then 'reload' the system with the ZFS / after its
been mounted so that the system functions as designed (ie. cron works etc)?

Steve