unable to offline a failing drive in a zfs RAIDZ

[Aryeh Friedman]

I have a raidz setup as per the handbook but when I attempt to
"offline" a failing drive it will not let me:

kate# zpool status -c
invalid option 'c'
usage:
        status [-vx] [pool] ...
kate# zpool status -v
  pool: storage
 state: ONLINE
 scrub: resilver completed with 0 errors on Mon Mar  1 17:36:48 2010
config:

        NAME        STATE     READ WRITE CKSUM
        storage     ONLINE       0     0     0
          raidz1    ONLINE       0     0     0
            ad7     ONLINE       0     0     0
            ad8     ONLINE       0     0     0
            ad9     ONLINE       0     0     0
            ad10    ONLINE       0     0     0
            ad12    ONLINE       0     0     0

errors: No known data errors
kate# zpool offline storage ad12
cannot offline ad12: no valid replicas