DFS. GOOD FAULT TOLERANCE SOLUTION.

Hi.
I have 15 sites connected with FR.
I have a MS sql server based application which write/read from files in server S1. Last week S1 went down for 120 min so the application did not work for 120 min and my life was miserable for the whole day.
I am trying to setup a fault tolerance system that allows the application keep working even if the server is down. I have done this before with SurviveIT, but I was wondering if I can setup DFS to replicate those file. There will only be one share that would be replicated. This 2 server would be in the same site. The DFS use the AD to replicate am i correct? Somebody told me that when the replication s happening files cant be open, is that true? is DFS a good option for fault tolerance in this case or is not the purpose of that service?

Thanks