Microsoft Clustering Concepts

In a Hyper-V environment, it may be useful to go over some of the concepts around clustering, and Microsoft’s solutions for providing clustering technology.

Clustering is done by using technology to group two or more servers together into a single functional unit. Traditional clustering techniques require the individual servers, or “nodes,” to be physically identical—that is, they need to have the same hardware configuration, memory size, CPU speed, etc. They also need to be identical in software configuration, with the same OS and (ideally) patch levels, and the same applications installed. In addition, all nodes of a cluster must have access to the same data storage, at the same speed; this is typically done with a high performance SAN.

There are two common types of clusters: fail-over and load-balanced. Failover clusters consist of a single node that typically handles all of the client requests, called the Primary node, and one or more nodes that are largely inactive unless the Primary node goes offline; these are called Secondary nodes. In a load-balanced cluster, all of the nodes participate actively in serving client requests. In most cases, a load-balanced cluster can also serve as a fail-over cluster, since one or more nodes of the load-balanced cluster can typically fail without the other nodes being impacted.

In any cluster, two major challenges present themselves: determining the status of a node member (particularly in fail-over clusters), and determining which node of a cluster currently controls a clustered application and its data. The first challenge is met with a heartbeat network, which is typically a physically separate set of network cards that communicate a signal, or heartbeat, to determine the status of each node. Data ownership is tracked by a data partition called the Quorum. The Quorum is a separate partition from the shared data, that also needs to be equally accessible to all nodes in a cluster. The quorum tracks which node is the owner of a given set of applications or data.

Source of Information : Elsevier-Microsoft Virtualization Master Microsoft Server Desktop Application and Presentation