There can be a number of scenarios you want to extend an LVM.

a. New Hard Drive

b. Free Space

c. Extended disk in a VM

If you just extended space, you have that as raw filesystem. So just open fdisk and create new partition and start working on the lvm:

`pvcreate /dev/sda```

vgextend "lvmname"  /dev/sda<x>

Find out the size of the extended Volume :

vgdisplay

From the information that you see as a result of above commands output, add the Free extends and Number of PE which will give the number of new extend.

Now run :

`lvm lvresize -l   /dev/VolGroup/lv_root ```

lvm lvresize -l 4900 /dev/VolGroup/lv_root