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Providing Fault Tolerance for Virtual
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You can utilize vSphere Fault Tolerance for your virtual machines to ensure business continuity with higher
levels of availability and data protection than is offered by vSphere HA.
Fault Tolerance is built on the ESXi host platform, and it provides continuous availability by having
identical virtual machines run on separate hosts.
To obtain the optimal results from Fault Tolerance you should be familiar with how it works, how to enable
it for your cluster and virtual machines, and the best practices for its usage.
This chapter includes the following topics:
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“Fault Tolerance Use Cases,” on page 391
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“Fault Tolerance Checklist,” on page 392
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“Preparing Your Cluster and Hosts for Fault Tolerance,” on page 393
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“Using Fault Tolerance,” on page 396
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“Viewing Information About Fault Tolerant Virtual Machines in the vSphere Client,” on page 398
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“Best Practices for Fault Tolerance,” on page 400
Fault Tolerance Use Cases
Several typical situations can benefit from the use of vSphere Fault Tolerance.
Fault Tolerance provides a higher level of business continuity than vSphere HA. When a Secondary VM is
called upon to replace its Primary VM counterpart, the Secondary VM immediately takes over the Primary
VM’s role with the entire state of the virtual machine preserved. Applications are already running, and data
stored in memory does not need to be re-entered or reloaded. This differs from a failover provided by
vSphere HA, which restarts the virtual machines affected by a failure.
This higher level of continuity and the added protection of state information and data informs the scenarios
when you might want to deploy Fault Tolerance.
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Applications that need to be available at all times, especially those that have long-lasting client
connections that users want to maintain during hardware failure.
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Custom applications that have no other way of doing clustering.
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Cases where high availability might be provided through custom clustering solutions, which are too
complicated to configure and maintain.
Another key use case for protecting a virtual machine with Fault Tolerance can be described as On-Demand
Fault Tolerance. In this case, a virtual machine is adequately protected with vSphere HA during normal
operation. During certain critical periods, you might want to enhance the protection of the virtual machine.
For example, you might be executing a quarter-end report which, if interrupted, might delay the availability
VMware, Inc.
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