Exchange 2003 to 2010 Coexistence

Hi Guys, a quick question

I'm rolling out 5 Exchange 2010 servers into a single Exchange 2003 environment next week. 2 Hub/CAS and 3 Mail servers and know the process to follow step-by-step to complete the server introduction for coexistence.

However, I have to present a risk and rollback plan if something goes wrong, but I cannot see through web research any issues that are likely to happen.

A couple of things to bear in mind is that there is no requirement for OWA or Active Sync services as this is an isolated site with a single Ex2003 server without any trimmings.

The 5 new Ex 2010 servers have been added to the domain and I am scheduled to install and configure Ex2010 next week.

What could go wrong and if so how would I roll back to the Single Ex2010 Server state?

In advance thank you for your advice.
CTCRMInfrastructure EngineerAsked:
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James HIT DirectorCommented:
I have a few questions:

1. Why the need to go from one to five servers? Do you understand the complexity of DAG?
2. How are you going to load balance between these servers?
3. Virtual or physical?
4. Backup of databases, what is your plan?
Simon Butler (Sembee)ConsultantCommented:
"2 Hub/CAS and 3 Mail servers"

If there is no ActiveSync or OWA access, why split the roles? That hasn't been best practise for some time (Exchange 2013 has dropped the hub transport role completely and CAS is just a proxy). You would be much better off with just all role servers.

With Exchange, you cannot really roll back the changes. The AD changes are a one way thing without causing significant damage to the domain.
The only thing you can roll back is mailbox moves, which would involve moving them back. If that isn't possible then you would be looking at a restore from a backup and then changing the AD account. However Exchange migrations are pretty risk free, I do 40 or 50 a year and I haven't had a single failure of the entire migration ever (odd mailboxes will fail, but that is to be expected).


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CTCRMInfrastructure EngineerAuthor Commented:
I have build 2 Win-2012 servers and will install both Hub and CAS server roles onto each server. I have also build 2 Mailbox servers. I am implementing a Barracuda (two-Arm) Network Load Balancer (Virtual Appliance) which will sit on our VMware Hypervisor so a virtual CAS Array with be configured and a minimum of two CAS servers are required.

The 2 MBX servers will be configure with a simple DAG configured to provide fault tolerance between both servers, we if one mail server folds then then other kicks in.

All new Ex2010 servers are virtual, all on the same subnet/site as Ex 2003 server, and users on this network will not be able to access there email via WebMail and will not be able to access email from the Public domain (External). The current Ex2003 server is physical (Server 2003) and end user do not have mobile or external access.

This is a secured site and such remote or external access to email is forbidden.

The planned process is as stands.
I have completed Pre-Site checks and Ex2003 server ensuring Native Mode etc.
The next step which will present a change to the production network is to introduce Exchange 2010 into the existing Ex2003 environment into Coexistence.

Before that I will be preparing AD and the Domain which will include Schema changes to ready itself for Ex2010.

I will then install and configure Ex2010 Hub/CAS roles onto the first 2 servers and upon completion I will install the MBX roles and configure the planned DAG to suit this small but critical environment.

I just need to know If there are any obvious issues that could arise, I don't believe there are as the current environment and requirement is straight forward and simple, and I haven't had issues in the past with more complex environments.

However, I can't afford to make any mistakes and would like to know if any problems could arise what the role back plan would be as changes to AD /Schema can be irreversible.
CTCRMInfrastructure EngineerAuthor Commented:
Simon Butler (Sembee)ConsultantCommented:
"I am implementing a Barracuda (two-Arm) Network Load Balancer (Virtual Appliance) which will sit on our VMware Hypervisor so a virtual CAS Array with be configured and a minimum of two CAS servers are required."

As you are using an external load balancer you DO NOT need to separate the CAS role.
The only time the CAS role needs to be separated out is when Windows Network Load Balancing is being used.
Furthermore, if it is a secure site with external access not required, then your separate CAS/Hub are going to be heavily under utilised. You are simply wasting resources.

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