Mirror rootvg

Make sure you have an empty disk, in this example its hdisk1
Add the disk to the vg via "extendvg rootvg hdisk1

#extendvg rootvg hdisk1

Mirror the vg via: "mirrorvg rootvg"

#mirrorvg rootvg

Adapt the bootlist to add the current disk, the system will then fail to hdisk1 is hdisk0 fails during startup

#bootlist -o -m normal

this will list currently 1 disk, in this exmaple hdisk0

#bootlist -m normal hdisk0 hdisk1

Run a bosboot on both new disks, this will install all software needed for boot on the disk

#bosboot -ad hdisk0
#bosboot -ad hdisk1