Users Guide

Designing for High Availability 21

Designing for High Availability

Planning and designing is a very crucial step in ensuring a highly available

environment that also provides the most isolation and best performance for

the HA solution. This section provides guidance on a few of the key scenarios

in failover cluster configuration.

Node and Disk Majority versus Node Majority

Cluster Configuration

As mentioned earlier, Hyper-V is dependent on the Failover Clustering feature

to provide HA capabilities. The Failover Clustering feature in Windows

Server 2008 offers multiple configuration models for clustering up to 16

physical servers. The difference between the clustering models is in which of

the cluster resources get to "vote" to decide whether or not the cluster is in a

highly available state at any given time. The most common and

recommended cluster configuration models are:

• Node and Disk Majority Cluster

• Node Majority Cluster

NOTE: A third type called Node and File Share may be suitable for certain

scenarios. However, that is beyond the scope of this document. For information on

all the cluster models, please refer to Microsoft website at

www.microsoft.com/windowsserver2008/failover-clusters.mspx.

Node Majority Cluster is a configuration in which only the servers that are

part of the cluster can vote, and Node and Disk Majority is a configuration in

which the servers and a single shared disk (SAN) resource get to vote. The

choice of the cluster model is dependent on the specific requirements of the

environment that the cluster is being deployed in.

Table 3-1. Comparison of Node Majority versus Node and Disk Majority

Node Majority Node and Disk Majority

Number of nodes Recommended for clusters

with an odd number of

server nodes

Recommended for clusters

with an even number of

server nodes