what is volume group
A volume group (VG) is a logical collection, or purposeful grouping, of computer storage space that may span multiple physical devices. It combines both physical and logical volumes into a single administrative element within UNIX&reg and LINUX&reg logical volume management (LVM). A physical volume may be an internal or external storage device. Logical volumes are concatenations, or chained lists, of storage space that might join portions of several physical volumes. Under LINUX&reg, the volume group is the highest level of abstraction, or visualization, in its logical volume manager utility.