First off, I have never tried to convert the rootvg into a scalable.
Reasons:
Usually rootvg should be sufficient for it's parameters. If you have application data etc. on the rootvg, you might want to think about adding additional disks and form a new VG on them to simply separate the OS from your application data.
Normally you want your rootvg for a production system as clean as possible which means that only OS stuff resides there with the one or other small exception.
If you want to give it a try anyways, I would do the following:
- Take a mksysb backup including all relevant file systems (check that you don't have excludes listed that might relate into a problem on a possible restore)
- Break the mirror
- Boot in service mode
- varyoffvg rootvg and try to issue the chvg and convert it to scalable