Making a case for Single VS Multi Roles

Would anyone who may have experienced this sceanrio help.
I am in the process of migrating to Exchange 2010 and had made a design as follows
1. 2 NLB CAS Servers
2. 2 Mailbox/HUB Transport server's.
This is a global setup that will have two Hubs one in the US and one in the UK. and above setup is per location
Close to implementation we needed to also implement Journaling and this is a 20k user base.I decided to change the architecture to:
1. 2 NLB CAS Servers
2. 2 HUB Transport Servers
3. 2 Mailbox Servers per location.
Our company has been growing and I was trying to avoid a situation that I will be forced to separate roles years or months down the road , when the choice of a separate HUB transport. Is this an over kill. I want to have a good reason for this in order to justify the purchase of additional licenses for the Operating systems (Windows and Exchange for the separated Roles).
jenkibabaSystem AdministratorAsked:
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Simon Butler (Sembee)ConsultantCommented:
I haven't split the roles out on any design I have done for over two years. That includes very large designs (15k plus).
The best practise is to now have all roles on all servers and just have lots of servers.

So I would deploy a core design of six servers total, three in each location.
In the US, server 1 and 2 would be in the US DAG, server 3 would be the passive for the UK.
In the UK, server A and B would be in the UK DAG, server C would be the passive for the USA.
Both DAGs A/A/P with enough hardware in all six server to take all users in that location.

Scale up as required for the user base.
Keep all of the machines identical, make the same changes to every machine using PowerShell.

Then deploy a hardware load balancer for each site.

Windows NLB is not recommended by the Exchange product team and I wouldn't even consider it for this number of users.

What are you journaling to? Another platform?

Simon.
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jenkibabaSystem AdministratorAuthor Commented:
Simon-thanks yes we are journaling to a third party. Did you say NLB is not recommended for EX2010? We were going to load balance the CAS in NA and EU and we are not using DAG.
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Simon Butler (Sembee)ConsultantCommented:
The Exchange product team don't recommend the use of Windows Network Load Balancing.

http://www.stevieg.org/2010/11/exchange-team-no-longer-recommend-windows-nlb-for-client-access-server-load-balancing/

Which is a good thing because it sucks.

Why aren't you using a DAG?

Simon.
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