I have 2 standard 2003 servers I’m migrating to 2012 R2. One is the Primary Domain Controller and is also running exchange 2003 ( I know, don't do this; read on please). The second is just a terminal server bit it’s the secondary domain controller.
My target 2012 servers are all 2012 R2 Standard Edition, in 3 separate VM’s. They are all joined to the current 2003 domain ready for migration (in fact, we are running a test migration of the accounting system right now on the new server). At the end of the domain & Exchange migration, the new PDC, Exchange 2010 and Terminal server will all be running on separate VM Servers so I’m essentially “splitting” the existing 2003 server in 2 and extracting out the PDC and Exchange 2010 into separate servers (all on the same domain of course). This particular installation will continue to run on premises only Exchange 2010. In order to install Exchange in this environment, it is necessary to do so by following a configuration that results in running a live Exchange migration to 2010 at the end of the installation. Basically a one shot deal. No problem so far but one big question:
Since the PDC has to be migrated as well (can't wait to finish off this 2003 server!!), the server roles have to be migrated to the new 2012R2 PDC and the old server will then have to be demoted yet still run exchange 2003 until all mailboxes are migrated (200+Gb’s of mailbox storage). Question: is it best (or required)to migrate the domain controller and roles BEFORE installing (which immediately begins migration) Exchange 2010 or is it necessary or best to install, migrate and wait for mailbox moves to complete on the Exchange 2010 server while it is running on the OLD domain PDC first then do the PDC migration. Which one’s first ?