How to unmirror a NW 5.1 Volume

Hello,

I used to have a procedure whereby I could unmirror a NW 5.1 volume by starting with Server -na -ns, loadstage 0, 1, 2(?) and then eventually load nwconfig from where then I could break the mirror. Disk 0 is defective, however, Disk 1 is OK so that I have to use it as the primary then install a good disk for secondary. I would appreciate if you could complete and correct the forgotten procedure, Thanks