Create a mirror on disk with valid data

[Victor Sudakov]

Colleagues,

gmirror(8) says that a mirror can be created from a disk with existing
data. However, other sources like 
http://ezine.daemonnews.org/200502/diskmirror.html 
say that the mirror device should be first partitioned, labelled and
formatted.

The second way seems to me more feasible. From experimenting with
different disks I have found out that (according to fdisk) the size of gm0
is several sectors smaller than that of ad0. I said to myself, that is
the overhead of the gmirror metadata.

How could it then be possible to create a mirror from a disk with
existing data, like the man page suggests?  The gmirror metadata could
then be overwritten with user data or vice versa.

Any input is very much appreciated. 

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN