Understanding the Layers of High Availability

Even in non-virtualized environments, there are multiple ways to achieve high availability for OS instances and applications. When you introduce virtualization into the mix with vSphere, you gain additional methods of providing high availability. Figure 7.1 shows these different layers.

At each layer, there are tools and techniques for providing high availability and business continuity:

• Examples of high availability at the Application layer include Oracle Real Application Clusters (RAC).
• At the OS layer, solutions include OS clustering functionality, such as Windows Failover Clustering (WFC) for Windows Server.
• The Virtualization layer offers a number of features for high availability, including vSphere High Availability (HA) and vSphere Fault Tolerance (FT).