Q about gmirror's "metadata sector"

[Johan Ström]

Hi

If i've understood correctly gmirror uses the last sector on the  
provider for a metadata.
If one uses http://www.onlamp.com/pub/a/bsd/2005/11/10/ 
FreeBSD_Basics.html to setup a gmirror'ed system, that is haveing a  
fully used disk
where the last sector is used (right?) and converting it to a  
gmirror, this will overwrite whatever is on the last sector, right?
This will probably not be overwritten on a non-full fs, but if the fs  
gets full later, is there any risk that this sector get's  
overwritten? Does one have to shrink the fs/slice manually or  
something to make sure this does not happend?

I haven't seen anyone mention this anywhere so im just curious to how  
it works

Thanks
Johan