I want to reinstall an old system to have combined root+usr. I have always used an lvm installation guide that was a "companion" to the handbook. That is it would tell you how to augment each handbook installation chapter for lvm (actually lvm2).
I can't find this documentation now on gentoo.org. There is a big wiki page, but that is different as are daniel's 2-volume "learning linux lvm". The closest I found is the raid+lvm quick install guide, but i would be happier with the one I have used often in the past. Any clues (I am emotionally prepared to learn that it is right there on the installation web page, but my eyes and search commands are deficient). thanks, allan