Exchange 2010 hub transport server load balancing -- what to watch for
Microsoft encourages failover clustering to provide fault tolerance and redundancy for Exchange
Server. However, neither the client
access server nor the hub transport server roles support failover clustering in Exchange 2010
-- only mailbox servers may be clustered.
To provide fault tolerance and redundancy for your hub transport servers, you must deploy one or
more additional hub transport servers. When you do, Exchange 2010 automatically distributes the
workload across your hub transport servers. This way, you don't have to worry about building a
cluster or configuring Exchange to use the new server.
While providing redundancy for the hub transport server role
When you register, you’ll also receive targeted alerts from my team of editorial writers and independent industry experts with the latest news, tips, and advice to help you do your job more efficiently and effectively. Our goal is to keep you informed on the hottest topics and biggest challenges faced by Exchange professionals today working with Exchange, Outlook and other related technologies.
Margie Semilof, Editorial Director
Premium Access
Register now for unlimited access to our premium content across our network of over 70 information Technology web sites.
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States.
Privacy
Dig Deeper
-
People who read this also read...
-
This was first published in September 2011
in
Exchange
2010 is fairly simple, there are a couple of important factors to remember when it comes to
effective load balancing.
Each mailbox server requires a hub transport server
The hub transport server resides at the Active
Directory-site level. This means that every Active Directory (AD) site that contains an Exchange
mailbox server also needs at least one hub transport server. You can't set up a single hub
transport server and expect it to service a multi-site Exchange Server deployment.
Because the hub transport server functions at the AD-site level, redundancy and fault tolerance
must also occur there. Deploying redundant hub transport servers help provide load balancing and
fault tolerance for a single site, not the entire Exchange Server organization.
The importance of Exchange Server 2010 Service Pack 1
The other important thing that you need to know about protecting the hub transport server role is
that if you’re using Exchange Server 2010 and have hub transport servers in multiple sites, Exchange
2010 Service Pack 1 (SP1) is essential. If you haven’t installed Exchange 2010 SP1, a hub
transport server failure will result in uneven workload distributions.
When Exchange 2010 routes messages to another AD site, it uses a technique similar to domain name system
(DNS) round robin to distribute the load among the hub transport servers in the remote site. For
example, if a remote site contains five hub transport servers, each server receives approximately
20% of the messages sent from the local site.
With that in mind, imagine that one of the five hub transport servers fails. The hub transport
servers in the local site are completely unaware of the failure in the remote site. Therefore, the
servers continue distributing the workload to all the remote hub transport servers. The connections
to the offline hub transport server fail, but once the failure is detected, Exchange routes the
messages to the next hub transport server.
The problem here is that the next hub transport server in line must take on the failed server’s
workload in addition to its own. This behavior is normal for sites with only two hub transport
servers, but for sites with three or more hub transport servers, it results in uneven load
balancing. Consider our example: If a failure occurred in a site with five hub transport servers,
one of the remaining servers would need to handle 40% of the total workload, while the three
remaining servers still received only 20% of the total workload.
Exchange 2010 SP1 is essential because it includes a feature called the Healthy Server Selector,
which tracks which Exchange servers are available. If a hub transport server in a remote site
fails, the Healthy Server Selector discovers the failure and prevents the local hub transport
servers from sending messages to the failed server until it comes back online. This helps Exchange
ensure that workloads are evenly distributed among the remaining hub transport servers.
ABOUT THE AUTHOR:
Brien Posey is an eight-time Microsoft MVP with two decades of IT experience. Before becoming a
freelance technical writer, Brien worked as a CIO for a national chain of hospitals and healthcare
facilities. He has also served as a network administrator for some of the nation’s largest
insurance companies and for the Department of Defense at Fort Knox.
Disclaimer:
Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.
