to add new disk to LVM
1) create a pv using "pvcreate /dev/sdx"
2) Then you can create a new vg on this PV using vgcreate commmand
else
If you want this PV to be a part of existing VG then you have to use vgextend command to include this PV in the existing VG
man pages will help you to get all the option you may want to use.
Thanks
Sri
abandon all hope, ye who enter here..