mirrorvg command like in AIX

I would like to see a mirrorvg command like in AIX that would allow us to make a bootable mirror of the root disk.

We are running into an issue with root being on a drive that is to small and we need to increase /var but no space is left. 

I know I can request another drive and add it to the rootvg and increase/resize the lv/fs as needed.

I like to keep rootvg on one disk not span multiple disks.

In AIX I can request a bigger drive.. mirror the rootvg... do some other commands (bosboot/bootlist) once its mirrored and then unmirror off the smaller disk and remove it. The system will boot just fine.

It would be nice to see this function in RHEL.

As of now I am being told I can only mirror the data disks not the rootvg and have it bootable.

This would be handy to use for cloning and updating to a new version of RHEL from say 5 to 6 or 7 etc. That way you have a recover point should you need it.

Might be good feature for patching a system too.

Clone then patch and have a fall back point if the patch breaks something.

We do this all the time on AIX.