LVM2 vs LVM1 on RH EL3
 

I have searched and I still have questions.

I see the a difference of DEVICE_MAPPER_SUPPORT.

What does this mean in detail?
Also, what are some of the other differences, constraints?

i'll admit i'm not familiar at all with LVM1, but i guess that's because it's obselete now and LVM2 is vatly preferable in all angles. I don't recall RHEL3 allowing any sort of LVM based installation though, maybe i'm wrong. if you're wanting to add it after the event though, still LVM2 all the way.

LVM2 will only work with kernel 2.6, whereas LVM1 will only work with kernel 2.4. So basically your kernel dictates what you use.