Like file servers, Microsoft Exchange servers are often deployed in remote offices to support local users. In many enterprises, an Exchange server is deployed to offices with as few as a dozen people in order to keep performance high. Since a single Exchange server can support thousands of users, deploying them in remote offices adds cost and complexity.

Why Do Exchange Servers Perform Poorly on WANs?

There are three reasons why Exchange servers perform so poorly on WANs. First, WANs typically have a tiny fraction of the bandwidth a server normally enjoys on a LAN. Second, WAN throughput is subject to the behavior of TCP, which can drastically reduce the performance of email access via Exchange. Third, the Exchange application protocol (MAPI, or the Messaging Application Programming Interface) is a highly chatty protocol that rides on top of TCP, creating additional latency delays. If you don’t fix all three problems, email access to and from centralized Exchange servers is going to suffer.

Riverbed has the Solution

Deploying Riverbed Steelhead appliances allows file servers to be consolidated without sacrificing performance for end users.

Centralizing Exchange servers from remote offices to data centers offers a host of benefits:

• Reduced complexity. Maintaining one or a very small number of Exchange servers is far simpler than maintaining dozens or hundreds of distributed servers. Additionally, email is not only critical to ongoing business operations, it also carries significant compliance requirements. Consequently, backup and retention of a single centralized server is much less complex and risky than distributed servers.

• Moderated WAN impact. Maximizing performance for all applications over the WAN is even more important as enterprises continue to deploy new applications to users around the world. Surges in email usage from a remote office, particularly first thing in the morning, often result in the WAN link being saturated. This can cripple other applications sharing the link. Steelhead appliances reduce WAN traffic dramatically, allowing other applications to perform better, even in the face of heavy email traffic.

• Addresses increased bandwidth usage from Outlook Cache Mode. Microsoft has released Exchange and Outlook 2003, which offer a new email-caching feature known as Outlook Cache Mode. Cache mode attempts to hide the effect of slower WAN throughputs by pre-emptively downloading new e-mails and their attachments. Unfortunately, it has the side-effect of increasing bandwidth consumption on the WAN, as all e-mails and their attachments will be downloaded the moment they are received, regardless of whether the e-mails are viewed by their recipients. Riverbed's SDR technology eliminates all repetitive byte patterns, for instance when multiple messages are issued as a result of e-mails addressed to aliases. Typically, SDR can result in an overall reduction of 60-90% of all bandwidth consumption, with or without the use of Cache Mode.
  
  For more information on the benefits of using Riverbed with Outlook 2003 Cache Mode, click here.