is there a way to run mining on different nodes for the same network? say I have a network of 3 nodes and i want that three should run miner.start
Yes, the ability to have different nodes mining on the same network is the whole point of mining. If your network is set up correctly (ie the nodes are all on the same network and synchronizing with each other) you should be able to run
miner.start() on each node and it should Just Work.
Just to clarify, AFAIK, there is no parallelization in mining. However, you can set up multiple nodes to use the same coinbase, hence increase your chance of mining.