Business-critical applications such as corporate e-mail must reside on systems and network structures that are designed for high availability. A highly available system reliably provides an acceptable level of service with minimal downtime. Downtime penalizes businesses, which can experience reduced productivity, lost sales, and reduced confidence from users, partners, and customers. By implementing recommended IT practices, it is possible to increase the availability of key services, applications, and servers. These practices also help to minimize both planned downtime (such as maintenance tasks or service pack installations) and unplanned downtime (such as server failure).

When planning for high availability of the Exchange 2010 deployment, the following recommendations should be taken into account:

• Plan for double failures.
• Do not over commit resources. Spread node failure across all the available nodes.
• Distribute database copies across nodes in a matrix.
• Use multiple 1 Gbps networks or 10 Gbps network.
• Design the high availability solution based on the business requirements (DR Plan, SLA, RPO, and RTO).

For planning High Availability for different Exchange Server Roles, follow the appropriate approaches below.

Based on the business High Availability requirements, the design needs to cover not only the Exchange components but also all the dependent components. Make sure that High Availability is catered for in all of the following components.

• Hardware components and their impact on performance and reliability
• Storage components
• Network Infrastructure
• Active Directory
• DNS
• Exchange Components