Achieving High Availability
As the information presented during the Windows installation states, Windows Server 2008 R2 is the most secure and reliable Windows version to date. It also is the most stable, mature, and capable of any version of Windows. Although we have seen similar claims in previous versions of Windows Server, we can be sure that Windows Server 2008 R2 is much better than previous versions for a variety of reasons.
An honest look at the feature set and real-world experience should prove that this version of Windows provides the most suitable foundation for creating a highly available solution. However, more than just good software is needed to be able to offer high availability for applications.
High Availability Foundation