How to cofigure san backup?

There is no single one way to do things. And so much depends upon nodes, adopters, topology, storage arrays and versions. There is no quick answer. I'm sorry to say that the only sensible answer to such a brief question is an equally brief answer of that it may best if you read a bit more and then come back with more questions that are more specific. Good luck. We will help more, but your question is too general, too open. :)