A couple of months ago Microsoft released an interesting whitepaper which changes how we position, or better “scale”, Exchange 2007 server roles. Especially the Client Access Server and Hub Transport Server role are 2 roles that seem to complement each other well as the Client Access Server uses more Memory resources while the Hub Transport uses more Processor and Disk resources. But still in many large scale deployments you will find these roles on dedicated servers because it had been the initial recommendation coming from Microsoft. Obviously this had a big impact because most likely you where considering high availability for your server roles which increased the number of servers dramatically for your deployment.

Today with this whitepaper Microsoft provides you with the testing matrixes and conclusions about combining the Client Access Server and Hub Transport Server role on a single server. In addition you will also get a clue on how many users/connections you can support on a given hardware configuration using of CAS/HUB load. Keep in mind that scaling a CAS server is difficult as it supports so many functions such as Outlook Web Access, Exchange Activesync, Outlook Anywhere & Exchange Web Services. Understanding how many users can be supported on a given CAS server can be tricky and you first need to determine the load distribution among these different services.

The 4 Cores/8GB Memory configuration was processing 24 messages/second at the same time and is also the server configuration used at Microsoft.

For more information read this whitepaper:

White Paper: Determining the Scalability of Combined Client Access and Hub Transport Server Roles in Exchange 2007
http://technet.microsoft.com/en-us/library/dd901772.aspx

Tonino Bruno | ICT Consultant | Pro-Exchange Community