I don't have a cluster yet, it's my first virtualized node. I only use KVM and I have 5 VPS, 2 with 2GB RAM and 3 with 1 GB RAM. It happens that at the charts I have something around 7GB RAM used (correct), but at 2 places it shows that I've used 15Gb:
1. CLUSTER RAM at the main screen
2. FREE RAM (When trying to create a new VPS)