In my last post I wrote about scaling Transport servers to meet the growing needs of an organization.  In this post I will look at the same topic for Client Access servers.

Client Access Servers

The role of the Client Access server for Exchange Server 2007 is to accept all non-MAPI client connections and communicate on their behalf with the appropriate mailbox server.

An example of this would be Outlook Web Access, where a user connects with their web browser to a webmail interface on the Client Access server instead of directly to their mailbox using the full Outlook client.

The Availability Service is another example of Client Access server functionality.

Most of the traffic that Client Access servers process uses SSL encrypted connections.  Encrypted traffic requires more processing resources than non-encrypted traffic.  This means that the most important resource for a Client Access server will be the processors, however memory and disk performance also play a role and can cause bottlenecks if not appropriately sized.

Processor Scaling

A Client Access server is recommended to start with at least 4 processor cores, but very smaller environments can perform well with just 1 or 2 cores, even with multiple server roles consolidated onto a single server.

A single server can scale up to 6 processor cores if necessary to handle load.  It is not recommended to scale beyond 6 cores per server.  If processor bottlenecks are found with 6 cores it is time to scale out to more Client Access servers.

Memory Scaling

For Windows servers memory is important for caching of data for fast access by the processors.  Insufficient memory would lead to excessive page file usage on the server and higher disk I/O, slowing the server down. Continue reading Scaling Up vs Scaling Out Exchange Server 2007 Roles Part 2 – Client Access Servers