6.0.1

Creating and Using vSphere HA
Clusters 2
vSphere HA clusters enable a collection of ESXi hosts to work together so that, as a group, they provide
higher levels of availability for virtual machines than each ESXi host can provide individually. When you
plan the creation and usage of a new vSphere HA cluster, the options you select affect the way that cluster
responds to failures of hosts or virtual machines.
Before you create a vSphere HA cluster, you should know how vSphere HA identifies host failures and
isolation and how it responds to these situations. You also should know how admission control works so
that you can choose the policy that fits your failover needs. After you establish a cluster, you can customize
its behavior with advanced options and optimize its performance by following recommended best practices.
NOTE You might get an error message when you try to use vSphere HA. For information about error
messages related to vSphere HA, see the VMware knowledge base article at
http://kb.vmware.com/kb/1033634.
This chapter includes the following topics:
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“How vSphere HA Works,” on page 13
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“vSphere HA Admission Control,” on page 23
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“vSphere HA Interoperability,” on page 29
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“Creating and Configuring a vSphere HA Cluster,” on page 32
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“Best Practices for vSphere HA Clusters,” on page 40
How vSphere HA Works
vSphere HA provides high availability for virtual machines by pooling the virtual machines and the hosts
they reside on into a cluster. Hosts in the cluster are monitored and in the event of a failure, the virtual
machines on a failed host are restarted on alternate hosts.
When you create a vSphere HA cluster, a single host is automatically elected as the master host. The master
host communicates with vCenter Server and monitors the state of all protected virtual machines and of the
slave hosts. Different types of host failures are possible, and the master host must detect and appropriately
deal with the failure. The master host must distinguish between a failed host and one that is in a network
partition or that has become network isolated. The master host uses network and datastore heartbeating to
determine the type of failure.
Sphere HA Clusters (http://link.brightcove.com/services/player/bcpid2296383276001?
bctid=ref:vSphereHAClusters)
VMware, Inc. 13