8.5 A brief history of clustering Exchange

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A cluster is a parallel or distributed system that consists of a collection of interconnected whole computers that are utilized as a single, unified computing resource.

-Gregory Pfister, In Search of Clusters, 2d ed. 1998.

Microsoft introduced Exchange clusters in November 1997, when it released Exchange 5.5, the Enterprise Version of which supported Wolfpack 1.0, or Windows NT cluster services. Exchange's implementation as a clustered application-at least one that could take full advantage of active- active clustering-was incomplete and not every Exchange service could run on a cluster. In particular, a cluster could not host many of the connectors to legacy messaging systems such as Microsoft Mail. However, you could deploy the basic messaging infrastructure on clusters and use them as mailbox servers.

The two servers in an Exchange 5.5 cluster must match in terms of CPU and memory, and you need licenses for the enterprise editions of Windows NT 4.0 (or Windows 2000) and Exchange 5.5 for both servers. Additionally, the hardware must be certified by Microsoft and be included on the cluster Hardware Compatibility List (HCL). Because Exchange 5.5 only supports active-passive clusters, one of the servers is usually inactive, although some customers used the passive server either to run file and print services or host another application. The net result was that an Exchange 5.5 cluster is an expensive solution that requires substantial expertise to deploy. Cluster state transitions were often extended, and although Microsoft worked to eliminate the causes (RPC timeouts and other software glitches) and improved matters in service packs, Exchange clusters never took off, and only a small percentage of customers evaluated them- with an even smaller percentage (estimated at less than 1 percent of corporate customers) moving into deployment.

The low penetration achieved by clusters had a domino effect, since ISVs were reluctant to make their code work on an Exchange 5.5 cluster. Thus, while you could deploy clusters as mailbox servers, you could not protect them against viruses or install other popular ISV software, such as backup agents, fax connectors, and so on. This situation gradually improved, as ISVs updated their code to support clusters, but the lack of third-party software presented a huge hurdle for potential cluster deployments to overcome.



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Microsoft Exchange Server 2003
Microsoft Exchange Server 2003 Administrators Pocket Consultant
ISBN: 0735619786
EAN: 2147483647
Year: 2003
Pages: 188

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