Converting back ti PV allow be to boot the old kernel again:
2.6.32-754.23.1.el6.centos.plus.x86_64
I'll change the new kernel command from:
kernel /vmlinuz-2.6.32-754.24.2.el6.centos.plus.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD console=hvc0 KEYTABLE=us rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto quiet rd_LVM_LV=VolGroup/lv_root rd_NO_DM
to
kernel /vmlinuz-2.6.32-754.24.2.el6.centos.plus.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD console=hvc0 KEYTABLE=us rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 crashkernel=auto noreboot rd_LVM_LV=VolGroup/lv_root rd_NO_DM
In PV mode all kernels shut down before the console appears.
IN HNV mode the new kernel displays:
Probing edd=off to disable
then shuts down after a few seconds and the older kernels shut down with just a blank screen.
Adding eff=off to the kernel line stops "Probing edd=off to disable"
appearing but the boot stops as before.
Maybe I'll try another Centos 6 VM to see if it does the same or if its just a problem with this VM.