In Vault, a volume group from which Vault selects backup images to duplicate. Selecting a source volume group restricts the search for images to those in that volume group rather than images in all volume groups. Usually, a source volume group is specified if your master server has access to multiple robots and you want to duplicate images that reside on media in one robot to media in another robot. The images that are read are in the source volume group in one robot; the images are written to media in the robotic volume group in another robot.
If you do not do duplication in Vault, you do not hve to specify a source volume group.