Enable vSphere FT on a cluster to benefit from fault tolerance on a VM in a VMware vSphere 6.7 infrastructure

6. Check network requirements, storage used and VM settings

When you want to enable vSphere Fault Tolerance (FT) on a virtual machine in your cluster, it is important to check a few details.

To begin, make sure the virtual machine is connected to a virtual network (port group) available on both the source and destination hosts.
If you are using a virtual distributed switch (vDS), this is certainly the case since all hosts use the same virtual switch.
But, if you are using virtual standard switches (vSS), you will need to ensure that the virtual network your virtual machine is connected to exists on the source host, as well as the destination one (where the secondary virtual machine will be created by vSphere Fault Tolerance).
In our case, our virtual machine uses the default virtual network "VM Network" which therefore exists on all our hosts.

Also make sure that the storage where the source VM is located is accessible by all hosts in the cluster.
In our case, we stored it on our "iSCSI DS 2" datastore.

As you can see, our "iSCSI DS 2" datastore is accessible by all hosts in our cluster.

As you can see, in our case, our cluster has access to our "iSCSI DS 1" and "iSCSI DS 2" datastores.
As explained previously, the source virtual machine and the destination virtual machine cannot be on the same datastore.
Hence the usefulness of having at least 2 accessible by all the hosts in your cluster.

Finally, make sure that this virtual machine does not use functions or devices incompatible with Fault Tolerance (see steps 3 and 4 of this tutorial).
To do this, click on the icon to modify the virtual machine settings.

Make sure you are not using any feature or device that is not compatible with Fault Tolerance.
Such as an RDM disk, for example.

7. Enable vSphere Fault Tolerance (FT) on a virtual machine

To enable vSphere Fault Tolerance (FT) on a virtual machine, select the desired virtual machine, then click: Actions -> Fault Tolerance -> Turn On Fault Tolerance.

Select the datastore where you want vSphere Fault Tolerance (FT) to create the secondary virtual machine.
In our case, we select our "iSCSI DS 1" datastore, because our source virtual machine is on our "iSCSI DS 2" datastore.

Note: as a reminder, the secondary virtual machine cannot be created on the same datastore as the main (source) virtual machine.

Select the destination host where you want vSphere Fault Tolerance (FT) to create the secondary virtual machine.
In our case, we select our host "esxi1", because our source VM is on our host "esxi2".

Warning : as a reminder, the secondary virtual machine cannot run on the same host as the main (source) virtual machine.

A summary of the secondary virtual machine configuration will be displayed.
Click Finish.

An "Enable Fault Tolerance" task will appear at the bottom of the window.

Once vSphere Fault Tolerance (FT) is enabled, a second task will appear: Start a secondary VM with Fault Tolerance.
You will also notice that once vSphere Fault Tolerance (FT) is enabled on a virtual machine, the virtual machine's icon will turn blue instead of white.

The red icon is because the virtual machine is being created. The virtual machine is not yet protected against the failure of the host hosting the secondary virtual machine.

Indeed, if you look at the bottom of the page, you will see that the Fault Tolerance status is "Unprotected" and that this message is displayed:

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Startup.
The virtual machine is powered on and has at least one secondary VM whose state is being synchronized with the primary VM.

As expected, in our case, the location of the secondary VM is "esxi1.informatiweb.lan".

Once the secondary VM is created and synchronized from the primary (source) VM, you will see that the "Start a secondary VM with Fault Tolerance" task is completed and the red light will have disappeared from the primary VM icon.

If you look at the storage of this main VM, you will see that 2 datastores appear for its storage.
In this case, this is the datastore used by the main VM, as well as that used for the secondary VM.

At the bottom of the window, you will see that the Fault Tolerance status has changed to "Protected".

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The virtual machine is running with Fault Tolerance protection.

As you can see, if we select our host "esxi2" and go to the "VM" tab, we can see that this hosts our main virtual machine (whose icon is blue).

If you select the main virtual machine, you see that it is running and therefore using CPU and memory resources.

If we select our host "esxi1" and go to the "VM" tab, we can see that this hosts our secondary virtual machine (whose icon is gray).

If you select the secondary virtual machine, you see that its screen is black and that it is not using CPU and memory resources.

This is because only one virtual machine is actually running. The other (the secondary VM) only has a copy of the CPU instructions, a copy of the RAM and a copy of the virtual hard disk to instantly take over in the event that the main VM is no longer available (because of of its host failure, for example).