Clustering tiers
An overhead concept to failover clustering that is important to understand is the different tiers at which clustering can benefit you. There are two levels upon which you can use clustering: you can take an either/or approach and use just one of these levels of failover clustering, or you can combine both to really impress your high-availability friends.
Application-layer clustering
Clustering at the application level typically involves installing failover clustering onto VMs. Using VMs is not a firm requirement but is the most common installation path. You can mix and match VMs with physical servers in a clustering environment, as long as each server meets the installation criteria. This application mode of clustering is useful when you have a particular service or role running within the operating system that you want to make redundant. Think of this as more of a microclustering capability, where you are really digging in and making one specific component...
