It need /boot/zfs/zpool.cache to locate zfs IIRC, and http://blogs.freebsdish.org/lulf/2008/12/16/setting-up-a-zfs-only-system/ export & import zpool to make /boot/zfs/zpool.cache up-to-date, so I guess exporting zpool delete the record in zpool.cache, then it can't locate your zpool. --Buganini