I am planning for a new Exchange 2010 deployment to replace our legacy Exchange 2003/2007 environments. This is part of a large merger so we are rebuilding Exchange from the ground up. With this merger we are going to have 3 production data centers, so we are planning to use this to our advantage with DR planning. My plans are to put 1 CAS/HUB server and 1 MBX server in data centers A and B and put 1 CAS/HUB and 2 MBX in data center C. Then put MBX-A and MBX-C1 in a DAG with the witness server in data center B, and put MBX-B and MBX-C2 in a DAG with the witness server in data center A. The idea behind this is so that if we lose a whole data center the failover will be automatic. My question is, does this topology make logical sense and will there be a problem with having the witness server completely off site from the DAG it is associated with, does the witness server store data or is it just a broker for the replication process. Thoughts?? Thank you.