Clearing out vdevs (can't create new zpool)

I have been poking around with our 16-port SATA RAID chassis (in JBOD
mode) with a fresh RELENG_7 internal build from Saturday.  I only had
half the disks {da0-7) at first, when I brought over the second set
(da8-15), I destroyed the existing pool and then tried to create a new
one with all 16 disks, and encountered this error:

-=-
# zpool create tank raidz da{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
cannot create 'tank': one or more vdevs refer to the same device
-=-

I can create one with the second set of disks (and destroy/create again)
but somehow I have some old vdevs sitting around which is preventing me
from using the first set of disks.  How can I clear them out?

Best Wishes - Peter
-- 
Peter_Losher_at_isc.org | ISC | OpenPGP 0xE8048D08 | "The bits must flow"