mongo DB - All nodes secondary
You can use the following instructions available at MongoDB's website:
http://www.mongodb.org/display/DOCS/Forcing+a+Member+to+be+Primary
If you have an even number of nodes, one answer is to remove one. Another answer can be to add an arbiter, which doesn't have a copy of the data but participates in the cluster purely for voting and breaks ties. This way you get odd vote numbers and guaranteed elections, but the availability/capacity of four nodes.