Ok, I've done what you recommended, I succesfully unmirrored my rootvg.

Here is the result of 'lsvg -l rootvg ' :

# lsvg -l rootvg
rootvg:
LV NAME TYPE LPs PPs PVs LV STATE MOUNT
POINT
hd5 boot 2 2 1 closed/syncd N/A
hd6 paging 256 256 1 open/syncd N/A
hd8 jfslog 1 1 1 open/syncd N/A
hd4 jfs 5 5 1 open/syncd /
hd2 jfs 220 220 1 open/syncd /usr
hd9var jfs 16 32 2 open/stale /var
hd3 jfs 6 12 2 open/stale /tmp
hd1 jfs 1 2 2 open/stale /home
hd10opt jfs 8 16 2 open/stale /opt

What is a 'stale' partition anyway?

Thx a lot for your help.

Regards