New high availability features in Exchange Server 2010
Exchange Server 2010 beta includes improvements to the server's high-availability (HA)
features. In this tip, Microsoft Exchange Server expert Brien Posey explains the new HA features in
Exchange 2010 as well as its clustered and non-clustered mailbox servers, scalability improvements
and more.
If you've used Exchange 2007's high availability features, you know that implementing HA can be
painful. For example, if you wanted to cluster a mailbox server, you must create that cluster up
front and it can only host the mailbox server role. If you start out with a non-clustered mailbox
server and decided you wanted to use clustering, there is no way to cluster the server. Instead,
you have to build a separate clustered mailbox server and move all of your mailboxes
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This was first published in June 2009
from the old
server to the new clustered server.
Exchange 2010 improves on how the server handles high availability. You no longer have to
cluster your mailbox servers at the time of deployment. In fact, Exchange 2010 completely does away
with the concept of a clustered mailbox server.
A new feature -- incremental deployment -- lets you implement site resilience and high
availability on an as needed basis. Furthermore, you can structure your Exchange 2010 organization
so that failover (or switchover) occurs at the database level rather than at the server level,
although server level failover and switchover is still an option.
Exchange Server 2007 allows you to host up to 50 databases on a single mailbox server. If a
problem occurs with a database, you need to failover the entire server -- even though 49 of the
databases were still healthy.
In Exchange 2010, failover and switchover occur at the database level. If a database failure
occurs, you can activate the database on another server that contains a replica of the database --
without affecting any of the functional databases that are hosted on the server.
By redesigning the way that clustering works in Exchange 2010, Microsoft has also improved
Exchange Server's scalability. Now, instead of being limited to hosting 50 databases per server, a
single server can host up to 100 databases.
Exchange 2010 also improves upon cluster size allowance. Cluster continuous replication (CCR)
limited Exchange 2007 mailbox servers to only two copies of a database -- one active and one
passive. In contrast, Exchange 2010 clusters can have up to 16 copies of a database -- one active
and up to 15 passive.
But this raises a few questions. Do you really need 16 copies of an Exchange database? Most
organizations won't need to create a cluster that large. Now you can increase the size of your
cluster as your business continuity requirements change.
Additionally, databases are no longer tied to a specific server. Exchange 2010 makes it simple
to move the active copy of a database from one server to another. Therefore, you won't have servers
that only act as hosts for passive database copies. In fact, Microsoft recommends that larger
organizations scatter active database copies multiple mailbox servers rather than having one server
that contains all active databases and other servers that contain only passive databases.
Since Exchange 2010 is only in beta, anything could change by the official release date. I don't
expect Microsoft to make any major architectural changes to Exchange 2010, it's possible that
clustering recommendations could change. In the meantime, I recommend that organizations that are
thinking about adopting Exchange 2010 consider how this new architecture will affect Exchange
Server backups.
About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable
Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information
Services (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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