I have /boot and /root that I have copy to a new one lvm volume.
I am try to boot my system through it but can't do that, it seems that all I need is to know what syntax to use on Grub2.
I have an uninteresting with lvm support in it, and I am still able to boot the system with the old partitions.
I didn't created a new grub.cfg file yet, since I want to test it without do it yet.
I need to know what syntax I need to use when I am try to boot from an lvm volume (that contain both /boot and /root as one partition).
I have Grub2 and Arch Linux if that helps.
Thanks.

You can't boot from lvm. The grub bootloader is very simplistic and has to be crammed into a very small amount of space, so can not contain enough code to read an LVM file system.

The default installation for Fedora installs a boot partition, and an lvm volume. The kernel needs to be loaded to assemble the LVM volume, and create the devices for the logical volumes. So /boot is kept separate. The same is true for most Raid volumes. The exception being mirrored raid, where grub can read from one of the disks. Even this isn't recommended.

So what is so special about Grub2 and lvm, as i have understnd it can boot through an lvm volume.
Read about it here:
https://wiki.archlinux.org/index.php/Grub2#LVM

dammit, i hate things changing!! I still wouldn't though. it might look ugly or something, but the simplicity you get from a dedicated /boot is significant.