Example -- Replacing a Submirror in a Mirror

# metastat d20
d20: Mirror
    Submirror 0: d21
      State: Okay        
    Submirror 1: d22
      State: Needs maintenance
...
# metadetach -f d20 d22
d20: submirror d22 is detached
# metaclear d22
d22: Concat/Stripe is cleared
# metainit d22 2 1 c1t0d0s2 1 c1t0d1s2
d22: Concat/Stripe is setup
# metattach d20 d22
d20: components are attached

The metastat command confirms that the two-way mirror d20 has a submirror, d22, in the "Needs maintenance" state. In this case, the entire submirror will be cleared and recreated. The metadetach command detaches the errored submirror from the mirror using the -f option (this forces the detach to occur). The metaclear command clears the submirror. The metainit command recreates submirror d22, with new slices. The metattach command attaches the rebuilt submirror, and a mirror resync begins automatically.

You temporarily lose the capability for data redundancy while the mirror is a one-way mirror.