Any of you 4x00 users can jump in any time now.
Discalmer: I have no idea any of these will work.
Looking at the cmd "co de config (individual/mirror/span/raid/xtra (=spare)) [dev,...]"
try "co de 10000 /xtra" ( this may make it a spare)
or "co de unmount 10000" to unmount it, may be needed before making it a spare.
to resysnc "co de resysn 60000"