Composite data source

hi~all:

I have 3 node,A,B&C,

If nodes A and B become unavailable, i want the applications restarted on node C,

So,i create a SHARED data source between A&B, and a MIRROR data source between B&C,

and then created a Composite data source Contains SHARED & MIRROR,

How to to execute the  sequence?MIRROR First? Or SHARED  have priority?

THANKS~