Exchange 2010 migration from 2003 Domain: Domain migration or Exchange migration first

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 ?
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Scott CSenior EngineerCommented:
Do the DC migration first.

Adding a Windows Server 2012 Domain Controller to an Existing Windows Server 2003 network

  Migrating Windows Server 2003 FSMO Roles To Windows Server 2012 R2

  Migrating DHCP From Windows Server 2003 to 2012 R2

 You will need to make sure the domain and forest level are both at 2003 before you can promote the 2012 server to a DC.
NinjaStyle82Systems AdministratorCommented:
Couldn't you bring up the new DC with the FSMO roles, then migrate exchange, then demote the old 2003 DC? I would migrate exchange, then bring the old DC offline.
ITOsoOwner/FounderAuthor Commented:
SchottCha: Can you please tell me why this is the way to go. I know the steps to do get the Domain to the 2012 R2 server; but what are the risks given the Exchange migration in the equation and the fact that once the Exchange installation is finished, Exchange migration happens right away (All connectors, etc. are pointing to the new Exchange server). Thanks!!
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ITOsoOwner/FounderAuthor Commented:
Frank: Yes, I could do so but the question is: what is the preferred or required or most sane order to do the migration, DC first or Exchange first? Exchange can migrate in the 2003 environment and I don't want to be on a new DC then start Exchange migration only to find out the old DC needs to be active or on line in order to accomplish this. It seems this may actually be the case and I want to be sure.
NinjaStyle82Systems AdministratorCommented:
I would migrate exchange before demoting the 2003 DC. otherwise i don't see why it would matter which new server you bring up first.
NinjaStyle82Systems AdministratorCommented:
as long as you are in 2003 functional level the two DCs can live side by side, especially if it's just temporary.
Scott CSenior EngineerCommented:
IMHO, moving the DC is an easy task and Exchange 2003 works just fine with a 2012 DC.

I like to get the easy small tasks out of the way so they are off my plate.  It's more a matter of personal preference.
AmitIT ArchitectCommented:
There is no sequence need to be followed to install Exchange, You can install DC or Exchange anytime. Installing DC and moving FSMO is faster compared to migrating Exchange. In your case, you follow this:

Install 2012 DC's
Install Exchange
Migrate all data from old server to new Exchange server
Once you are done with migration, now you decom exchange first
Finally decom your old DC

Remember your new server should also be a GC and in same site, where you Exchange is currently located. If you have AD integrated DNS, make sure to install that also.

Let me know, if any other query or doubt.

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