Inherited a situation where there is one Exchange 2007 Build 83.6 server running on Win2008R2, acting as witness, and hub transport and yes is a file server too. In addition there is relays, email and service accts that need to be moved to Exchange 2013.
Presently there are two Exchange 2013 cu3 servers that are part of a DAG that also run on Win 2008r2... We wish to add another node to the DAG, and move the witness to another server.
Do I need to also add a CAS Exchange 2013 server to replace the Ex 2007 server?
Can this server also act as the Witness?
What would be the best practices for this senario. All of these machines are VM's.