The consistent_hash selection strategy allows for a weighting of the parents. So, a config like,
would have p1 placed in the ring twice as many times as p1, and thus should received 2x more URIs as p1. (Note that traffic associated with URIs can vary considerably, so this weighting can be randomly associated with traffic levels).
This weighting should be extended to the round robin selection strategies (strict|true)-- weighted round robin is a common load balancing strategy. In these cases, the weightings would likely cause selection to cycle amongst the parents such that each target would roughly end up with N/(sum of Ns) % of the total traffic.