6.0.1

Providing Fault Tolerance for Virtual
Machines 3
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.
Fault Tolerance Protection for Virtual Machines
(http://link.brightcove.com/services/player/bcpid2296383276001?
bctid=ref:video_fault_tolerance_protection_vms)
This chapter includes the following topics:
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“How Fault Tolerance Works,” on page 45
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“Fault Tolerance Use Cases,” on page 46
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“Fault Tolerance Requirements, Limits, and Licensing,” on page 46
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“Fault Tolerance Interoperability,” on page 47
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“Preparing Your Cluster and Hosts for Fault Tolerance,” on page 49
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“Using Fault Tolerance,” on page 51
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“Best Practices for Fault Tolerance,” on page 55
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“Legacy Fault Tolerance,” on page 57
How Fault Tolerance Works
You can use vSphere Fault Tolerance (FT) for most mission critical virtual machines. FT provides continuous
availability for such a virtual machine by creating and maintaining another VM that is identical and
continuously available to replace it in the event of a failover situation.
The protected virtual machine is called the Primary VM. The duplicate virtual machine, the Secondary VM,
is created and runs on another host. The Secondary VM's execution is identical to that of the Primary VM
and it can take over at any point without interruption, thereby providing fault tolerant protection.
The Primary and Secondary VMs continuously monitor the status of one another to ensure that Fault
Tolerance is maintained. A transparent failover occurs if the host running the Primary VM fails, in which
case the Secondary VM is immediately activated to replace the Primary VM. A new Secondary VM is started
and Fault Tolerance redundancy is reestablished automatically. If the host running the Secondary VM fails,
it is also immediately replaced. In either case, users experience no interruption in service and no loss of data.
VMware, Inc.
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