6.0.1

Using Fault Tolerance with DRS
You can use vSphere Fault Tolerance with vSphere Distributed Resource Scheduler (DRS) only when the
Enhanced vMotion Compatibility (EVC) feature is enabled. This process allows fault tolerant virtual
machines to benefit from better initial placement.
When a cluster has EVC enabled, DRS makes the initial placement recommendations for fault tolerant
virtual machines and allows you to assign a DRS automation level to Primary VMs (the Secondary VM
always assumes the same setting as its associated Primary VM.)
When vSphere Fault Tolerance is used for virtual machines in a cluster that has EVC disabled, the fault
tolerant virtual machines are given DRS automation levels of "disabled". In such a cluster, each Primary VM
is powered on only on its registered host and its Secondary VM is automatically placed.
If you use affinity rules with a pair of fault tolerant virtual machines, a VM-VM affinity rule applies to the
Primary VM only, while a VM-Host affinity rule applies to both the Primary VM and its Secondary VM. If a
VM-VM affinity rule is set for a Primary VM, DRS attempts to correct any violations that occur after a
failover (that is, after the Primary VM effectively moves to a new host).
Preparing Your Cluster and Hosts for Fault Tolerance
To enable vSphere Fault Tolerance for your cluster, you must meet the feature's prerequisites and you must
perform certain configuration steps on your hosts. After those steps are accomplished and your cluster has
been created, you can also check that your configuration complies with the requirements for enabling Fault
Tolerance.
The tasks you should complete before attempting to enable Fault Tolerance for your cluster include the
following:
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Ensure that your cluster, hosts, and virtual machines meet the requirements outlined in the Fault
Tolerance checklist.
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Configure networking for each host.
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Create the vSphere HA cluster, add hosts, and check compliance.
After your cluster and hosts are prepared for Fault Tolerance, you are ready to turn on Fault Tolerance for
your virtual machines. See “Turn On Fault Tolerance,” on page 53.
Fault Tolerance Checklist
The following checklist contains cluster, host, and virtual machine requirements that you need to be aware
of before using vSphere Fault Tolerance.
Review this list before setting up Fault Tolerance.
NOTE The failover of fault tolerant virtual machines is independent of vCenter Server, but you must use
vCenter Server to set up your Fault Tolerance clusters.
Cluster Requirements for Fault Tolerance
You must meet the following cluster requirements before you use Fault Tolerance.
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Fault Tolerance logging and VMotion networking configured. See “Configure Networking for Host
Machines,” on page 50.
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vSphere HA cluster created and enabled. See “Creating and Configuring a vSphere HA Cluster,” on
page 32. vSphere HA must be enabled before you can power on fault tolerant virtual machines or add a
host to a cluster that already supports fault tolerant virtual machines.
Chapter 3 Providing Fault Tolerance for Virtual Machines
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