I’m writing a series of blog posts going over some of the things we learned at the Microsoft Exchange Conference this year. The next announcement from MEC I want to highlight is Microsoft updated sizing guidance for Exchange 2013 SP1. There are two main areas around which Microsoft has updated the guidance for Exchange 2013 SP1 server sizing; CAS processors and pagefile.
With this introduction of Mapi/Http, it is necessary to update the guidance for processor sizing on the CAS role. Mapi/Http will cause a fairly significant increase in the rate of requests from clients to the CAS roles over the request rates from the same clients connected via Rpc/Http. This increased number of requests means that the recommendation for CAS processors goes from 1:4 CAS to Mailbox server cores if your clients are using Rpc/Http to 3:8 CAS to Mailbox server cores if your clients are using Mapi/Http. That is a 50% increase.
I do need to stress that Mapi/Http is not enabled by default, and at this time there is not really a very compelling reason for an on-premises Exchange organization to turn on Mapi/Http. In the future as Microsoft starts to implement the other improvements that will be made possible by Mapi/Http, administrators will need to consider the impact to their servers of turning on Mapi/Http.
The Exchange 2013 server roles requirements calculator published by the Exchange team has been updated to reflect this new guidance for CAS processors.
The previous guidance from Microsoft about the pagefile size for an Exchange server was equal to the size of the installed RAM plus 10 MB. Exchange 2013 deployments can require some pretty high amounts of RAM. Exchange 2013 servers with 64, or even 128 gigabits of RAM are not uncommon but a pagefile of 128 gigabits is going to take up a huge amount of space on your system drive and will provide little to no benefit.
With that in mind, Microsoft has updated the pagefile guidance for Exchange 2013 deployments to be the smaller of RAM + 10MB or 32BG + 10MB (32,778 megabits). That should save a bit of space on your Exchange 2013 system drives.