How Exchange Server ActiveSync (EAS) scales for us
Published Dec 13 2004 12:16 PM 1,195 Views

This afternoon I received the Exchange Server ActiveSync (EAS) usage statistics for the month of November.  Our friends at MS IT told me that our internal user base is growing:  we are at about 7000 unique users at Redmond!!! These users were served about 900,000 connections. Woah!

Some may think that it must take lots of resources to support synchronization for 7k devices, this is indeed NOT the case (at least with EAS)…you should read the MS IT scalability paper, which describes what environment MS IT is running and how they are using two servers to support not only the 7k devices, but also OWA, OMA and RPC/HTTP for the entire Redmond campus!!! (http://www.microsoft.com/windowsmobile/business/whitepapers/scalability.mspx)  

As I was looking at the stats I remembered the discussions that I recently had with many Exchange administrators at IT Forum few weeks ago about scalability and reliability of EAS in Exchange Server 2003.   As you all probably know Exchange Server ActiveSync is a “standard” web server application, it runs along with Outlook Web Access.  The critical point is that EAS is a stateless server: each request from the client is processed independently.  There are several benefits that are derived from this approach, to name few:

      - Users are not bound to any server, when a server is unavailable the client request can be processed by any other available resource

      - There is no requirement for any affinity if you deploy a network load balance solution

      - As your deployment grows, you simply scale “out” and add an additional Exchange Front-end server and get even more devices to connect

There is one trick that you can use to further improve the reliability of the EAS solution.  By default, OWA and EAS share the same default application pool.  You can create a new application pool and bind the EAS website (or virtual directory) to the newly created application pool.

- Max Ciccotosto

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