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Troubleshooting slow Outlook Web Access (OWA) performance

Do your Exchange mobile users struggle with slow Outlook Web Access (OWA) server performance? The initial cause may not be your OWA server, but instead a firewall or infrastructure issue. To pinpoint the root cause of slow OWA server performance, use the Performance Monitor. If there isn't one particular issue causing slow performance, the entire server may be unable to support a normal workload. Replacing the server or using network load balancing can fix this.

If you have several mobile users accessing your Exchange Server organization through Outlook Web Access (OWA), your front-end server or client access server (CAS) may become a bottleneck. Troubleshooting OWA performance problems is complex, but boosting OWA performance is simple. This tip explains how.


Is OWA really causing your performance problems?

If you want to improve OWA's performance, you first must determine whether or not it's the root cause. Although OWA can become overloaded, another common source may be an underlying component.

Check your Internet connection and your firewall. In real-life situations, these two components can be major contributors to OWA performance problems. All mobile users are competing for Internet bandwidth when accessing the OWA server. Therefore, unless you have sufficient bandwidth to support all of your mobile users -- and anything else that you might be using the connection for -- your clients will experience slow performance.

Firewalls can contribute to performance problems. For instance, one organization I worked with was constantly being attacked by hackers. The organization had an advanced firewall or intrusion detection software (IDS) that prevented most attacks, but the firewall could only process a certain number of packets per second. Because the firewall had to process several inbound packets, legitimate users complained about OWA's extremely slow performance. Ultimately, the organization had to invest in a firewall that could keep up with the inbound traffic.

If your underlying infrastructure appears to be functioning well, I recommend examining your OWA server. Some basic performance monitoring techniques will help determine the cause. Make sure that your system has plenty of free CPU, memory and disk resources, and that the network connection to the back-end Exchange organization isn't saturated (although this is an unlikely cause).

If your OWA server is the cause of user performance problems, then the Performance Monitor will alert you to one of two things.

  • One particular component in the OWA server is causing the bottleneck. For example, the server may be low on memory, or the server's CPU may be inadequate for servicing the current workload. In such cases, upgrading the problematic component will fix the problem.
  • There may not be one particular issue causing your performance problems. Instead, the entire server may be inadequate for supporting the normal workload. If this happens, you can either replace the server or use a load-balancing solution.

Load balancing an OWA server

OWA is an ideal candidate for load balancing. The OWA server itself doesn't store any data; therefore, you can run multiple OWA servers in parallel to distribute the workload. This enhances performance and adds a degree of fault tolerance.

Network load-balancing capabilities are built into Windows, so you won't have to buy any third-party software. You will, however, need Windows and Exchange Server licenses for each additional OWA server.

When you configure network load balancing, you essentially create a cluster of up to 32 OWA servers. Each server retains an individual IP address, but there's also a cluster-specific IP address that all OWA servers within the cluster share. Use this address in the DNS record for your OWA implementation.

About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional award for his work with Exchange Server, Windows Server, Internet Information Server (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.

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