How to remove non-redundant Vdev from zpool( only inactive hot spares or cache devices can be remov

 Hi,

Please help me to remove non-redundant Vdev from zpool.

root@SFV240-NODE1 # zpool create mypool mirror c1t44d0 c1t44d1
root@SFV240-NODE1 # zpool status
  pool: mypool
 state: ONLINE
 scrub: none requested
config:

        NAME         STATE     READ WRITE CKSUM
        mypool       ONLINE       0     0     0
          mirror     ONLINE       0     0     0
            c1t44d0  ONLINE       0     0     0
            c1t44d1  ONLINE       0     0     0

errors: No known data errors
root@SFV240-NODE1 # zpool add mypool c1t44d2
invalid vdev specification
use '-f' to override the following errors:
mismatched replication level: pool uses mirror and new vdev is disk
root@SFV240-NODE1 # zpool add -f mypool c1t44d2
root@SFV240-NODE1