Chunks are now stored as 3 groups of 2 chunks. So 1st group is primary, 2nd group is backup (in case of failure) and third group is sacrificial. The sacrificial basically has farmers holding data we don’t need. The amount of this held in relation to the number of primary chunks tell us the network storage health (balance). So basically we have 50% more data copies than needed. We can lose all of that but then it’s dangerous, so the resource balance kicks in when we see this is vanishing.
Nodes will delete sacrificial data to make room for the other types. This deletion starts to increase farming rates and as we lose more we increase the rate more (farming rate == amount of reward)
Group size is the size of the group in which data can be stored, so with a group size of 32, data can be stored on the closest node to the data and, as the group changes, it stays there (the node may no longer be closest; in probability, it will not be). If that nodes leaves or goes out of the group then the members of the group (NaeManagers) will relocate the copy to (again) the closest node. This is continuous.
I hope that helps.