Any idea about EMC RepliStore on 2 Windows Server Cluster

I have 2 Windows Cluster Server, which have EMC RepliStore installed in them. I dont have much idea about RepliStore provided that, it constantly copies data on one another, when ever any changes happens to the data.

My main question is right now, that both servers is falling short of storage capacity. I am planning to add a bigger LUN, on to both and copy of that data from smaller drive to the bigger new LUN which I am going to map on the server.

Is their anything that I need to know before I do anything and also from EMC RepliStore point of view. Provided that, I need to take down the entire application on both of the server down and do every thing.

Thank You