The Exchange team at EHLO released a nice paper in the TechNet library on the subject of Client Access Server workloadson Exchange Server 2010. This paper is to illustrate the effect of using different client modes with different protocols (i.e. Outlook Cached Mode yes/no, Outlook Anywhere, OWA, POP, IMAP, ActiveSync). It also shows the differences between using Windows Server 2008 SP2 and Windows Server 2008 R2 in combination with these protocols.

Some examples:

• For Outlook Anywhere, the CPU usage per user on CAS servers almost quadruples around 6.000 users when comparing SP2 against R2;
• For Outlook Anywhere, CPU usage for AD/Hub/Mailbox starts to flatline at 3.000+ users;
• For Outlook Anywhere, as you probably already knew, it is recommended to use Windows Server 2008 R2;
• For IMAP, the mailbox size is of big influence on the CPU usage;
• For POP3, the number of Mailbox IOPS drops as the number of users increases;

They also perform a comparison between Exchange Server 2007 SP1 and Exchange Server 2010 regarding IMAP. For example, CPU usage on CAS servers when using IMAP clients is reduced by 40% and memory bij 30%.

What does puzzle me is that in some comparisons they left out certain measurements and some graphs are missing scale information. For instance, the graph for Total CPU consumption for IMAP4 has SP2 start at 37.000 while R2 starts at 12.000. Why? Did SP2 produce some weird results or is it off the scale? The paper doesn’t mention it.

Nevertheless, interesting stuff.

You can read the whitepaper here. Unfortunately, there’s only an online version of the paper.