Look before you leap

There’s a great deal of talk these days about migrating directly to Exchange 2010 instead of jumping first to the 2007 version of the platform.  The arguments for and against this got more complicated when Microsoft did a reversal for support and announced that 2007 would be able to run (at some future point) on Server 2008 R2.  This effectively extended the support cycle of 2007, which means that a slightly older, and more thoroughly tested and widely installed, version is a legitimate option going forward.  That being said, many clients are opting to just go to Exchange 2010 from whatever they’re on now, skipping 2007 if it isn’t already in place.

I’m going to avoid discussing the pros and cons of going to Exchange 2010 directly in this particular post (that’s fodder for quite a few additional posts though).  Let’s just say that you’re jumping from an earlier version directly to 2010 and go on from there.  While most of the process isn’t too bad overall, there are a couple of sticking points that you’ll need to have sorted out before you make the move.  In smaller organizations, these are pretty easy issues to take care of, but on large-scale roll-outs, they can be a problem.

First, make sure your domains are at least at Server 2003 native functional domain levels.  Most of you are already there, but just in case you had a few NT servers hanging around, be ready for this one.  As long as all your servers are 2003 and up, making this change doesn’t have a lot of impact on your domain.  You can find out about the impact of raising Domain Functional Levels in this TechNET article.  So, what if you DO still have Exchange 2000/Windows 2000 servers in your environment?  You need to upgrade to Exchange 2007 as an interim step to 2010.  Since the Exchange 2000 life-cycle is definitely over (and has been for a while), Microsoft offers no method of co-existence between Exchange 2000 and Exchange 2010 – migration or otherwise.

Once your domain is prepped to 2003 or 2008 native mode, you then must plan to keep your old Exchange infrastructure long enough for the migration to occur.  That’s because the Mailbox systems for one version of Exchange can’t talk to any other in most cases.  So a 2003 Mailbox Server can’t talk directly to a 2010 Mailbox Server without some assistance.That assistance is in the form of Bridgehead servers (2003) or Hub/Transport and Client Access Servers (2007). You will need to have at least one of each for each Site you have set up in Exchange/AD.  One note, this has nothing to do with the migration itself, this is all about the period of co-existence you’ll need to go through until everyone is on the 2010 architecture.

After you have upgraded your Domain Functional Level and set up your front-end server systems, you can begin the process of installing the first of your Exchange 2010 server systems.  Start with the Hub/Transport and Client Access roles (unless you are installing them on the Mailbox Role server itself) to allow for message routing to get set up.  This lets mail flow between the 2010 and legacy front-end servers, so when you start moving mailboxes, you don’t lose mail connectivity.

Finally, once you’re sure mail is flowing correctly and that no one is about to get lost in the shuffle, take one more backup of the legacy systems (just to be safe) and start your migration.

You can find a guide to preparing for and deploying Exchange 2010 at this TechNET site.  Along with other blogs and Microsoft sites, this should be required reading before you even download the software and play with it in a lab.  With a migration that includes a period of co-existence with earlier versions of Exchange; careful, proper planning is not a nice-to-have thing.  It is a solid requirement that must not be overlooked or under-appreciated.