NetApp Snapshots

Hi Guys,

Im wondering if someone can tell me what im seeing below. I understand they are the snapshots however whats confusing me is the "Total Size" and "Cumulative Size". Firstly its a 2TB drive and im not sure show the total size of this snapshot is 28.17MB and the cumulative is 125.52MB, Checked against the others and Nightly 2 is very different. Can anyone let me know where its dragging these figures from just so i can understand it please? Thanks for your help! Probably such a newbie question!