gmirror clearing configuration

[Dave]

Hello,
    I'm trying to set up raid1 on fbsd 5.4-RELEASE no patches yet installed 
just a vanilla release box. I've messed up somewhere, the primary drive is 
smaller than the secondary drive and i'm using Ralf's second procedure. My 
problem is i can't clear the metadata from either the first or second drive 
so i can start again, i load gmirror then issue a gmirror clear and it says 
it can't clear the metadata. Any help appreciated.
Thanks.
Dave.