I am experimenting most suitable cloud scheme. Cluster has three status Green, Yellow and Red. It is good to have Green cluster. I did so many experiments to choose this and finally get to the conclusion. It is always good to have N = R + 1. Where N is number of nodes and "R" is Number of replicas. So if you want to have 3 replicas than you should go for 4 nodes to keep the cluster status Green Which seems to me good.
I'm not sure if i am explaining in the right direction. Suggestions from someone experienced are highly appreciable.