geometry does not match label

[Robin Becker]

I'm just setting up a software raid mirror using geom; everything seems to be 
working fine and the mirror is slowly synchronizing.

Because of cabling constraints this is a mirror rather than a duplex (I haven't 
used mirror before) so the gm0 components are ad0/ad1 rather than ad0/ad2. In 
dmesg I see
......
GEOM_MIRROR: Device mirror/gm0 launched (1/2).
GEOM_MIRROR: Device gm0: rebuilding provider ad1.
GEOM: mirror/gm0s1: geometry does not match label (16h,63s != 255h,63s).
......
Trying to mount root from ufs:/dev/mirror/gm0s1a
......

anyone know if I should worry about the "geometry does not match label" message?
-- 
Robin Becker