High Availability and Clustering Technologies
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High Availability and Clustering Technologies
Availability refers to a level of service provided by applications, services, or systems. Highly available systems have minimal downtime, whether planned or unplanned. Availability is frequently expressed as the percentage of time that a service or system is available, for example, 99.9 percent for a service that is unavailable for 8.75 hours per year.
To improve availability, you have to implement fault tolerance mechanisms to mask or minimize the impact of failures of the components and dependencies of the service. Fault tolerance is achieved by implementing redundancy to single points of failure components. When planning for Microsoft Exchange availability, consider all components that are part of the messaging infrastructure. Some components could also be other services that have subcomponents.
The messaging service availability is determined by the availability of each component that is part of the infrastructure.
Microsoft Exchange Server 2007 includes new features that can reduce costs and increase uptime:
- Local Continuous Replication
- Cluster Continuous Replication
- Single-Copy Clusters