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The topology presented in Figure 2.3 does offer options to improve scale and support a high level of performance. However, it lacks a key factor that should not go overlooked when implementing the solution: availability. In most cases no one considers availability until a disaster occurs. For example, what happens if the SQL Server that hosts the SharePoint databases shuts down? How much downtime will accumulate prior to the system coming back online? As a result, in addition to installing and configuring more web and application servers for scale and high availability, additional servers should be added to ensure that a high level of availability is maintained for all parts of the configuration.

In Figure 2.4, the Domain Controller, SQL Server and Analysis Servers are single machine. This typically introduces a problem of availability. To ensure that the servers are protected in the event of a failure or disaster means implementing some type of High Availability (HA) or Disaster Recovery (DR) solution. You could use clustering for the domain controller and a mix of clustering an AlwaysOn for the SQL Server Analysis Server and the SQL Server Database Engine. Both clustering and AlwaysOn are technologies that provide HA and DR at server and database levels. Implementing this topology almost doubles the number of servers. Figure 2.5 represents a sample of an HA solution.

Figure 2.5 Sample Microsoft business intelligence HA server topology

The SQL Servers and domain controllers are doubled to ensure that the environment remains online in the event of a server failure. What is not represented in the figure is an additional environment that protects against the loss of the primary data center. This addition would even further extend server requirements and increase capital investments. Although costly, this added environment could provide more protection and availability in the event of a major disaster.