7.4 Cluster Support for Exchange 5.5

When Microsoft set out to provide clustering support in Exchange Server 5.5, the development team had two primary goals. First was to increase the availability of Exchange Server by adding clustering support. Second was to provide protection from hardware failures. Distributed processing, load balancing, and data backup were not part of these original goals. As a result, Exchange Server 5.5 provided only basic failover capabilities when paired with Microsoft Cluster Service. Exchange Server 5.5 Enterprise Edition implementssupport for MSCS using the Service Failover mode described earlier. One generic resource DLL is used for each Exchange service (i.e., Information Store, Directory Service, Message Transfer Agent, and System Attendant). This allows for individual services to be brought down without causing complete failover, and it also isolates services, which helps ease troubleshooting.

Functionality supported within Exchange Server 5.5 in a clustered environment can be classified into two categories: supported services and nonsupported services.

Supported services include those required to provide basic Exchange Server functionality such as the Information Store, Directory Service, Message Transfer Agent, and System Attendant. In addition, the Internet Mail Service and the Internet News Service support clustered functionality (with the exception of the dial-up mode of these services). These supported services provide automatic startup on failover, automatic recovery processing, and global registry updates when moving between cluster nodes. The remaining Exchange Server 5.5 functionality falls into the nonsupported category. The following table lists some of these services and provides known "gotchas" and tips if...