VMware Fault Tolerance is a component of VMware vSphere and it provides continuous availability to applications by preventing downtime and data loss of Virtual machines in the event of ESX server failures.

What is the name of the technology used by VMware FT?

VMware FT using a technology called vLockstep technology

What are requirements and Limitattions for ESX hosts & infrastructure components to run FT protected virtual machines in Vsphere 4 & 4.1?

Please refer my blog post on ESX Host -Infrastrcuture Requirements & Limitations for VMware Fault Tolerance to see the ESX requirements for VMware FT.

What are Requirements and Limitations for Virtual Machine to Enable FT ?

Please refer my blog post on Virtual Machine Requirements for VMware Fault Tolerance

How do i check my host for FT compatibility from vSphere client?

One way from vSphere client is to run the cluster complaince check from profile compliance tab of  your cluster. The below checks as specified below will be performed as part of the compliance check.

Validate that Fault Tolerancelogging NIC speed is at least 1000 Mbps.
Validate that power management is supported on the host
Validate that Fault Tolerance logging is enabled.
Validate that VMotion NIC speed is at least 1000 Mbps.
Validate that all the hosts in the cluster have the same build for Fault Tolerance
Validate that the host hardware supports Fault Tolerance.
Validate that VMotion is enabled.
Validate that at least one shared datastore exists

Another way is to check the summary tab of the ESX/ESXi host, “Host Configured for FT” yes or NO.

What is FT Logging Traffic?

FT logging is the one of option in VMkernel port setting which is similar to enable vmotion option in the vmkernel port. when FT is enabled for the virtual machine, all the inputs (disk read.. wirte,etc..) of the primary virtual machine are recorded and sent to the secondary VM over via FT logging enabled VMkernel port.

How to Enable FT Logging in VMkernel Port?

GO the ESX host -> Configuration-> Networking -> Properties of Virtual switch with the VMkernel portgroup configured

Click on VMkernel Port -> click on Edit -> General tab ->  select the Fault Tolerance Logging -> click on OK.

How do you configure or enable FT for the virtual machine ?

FT can be enabled only per virtual machine basis not at the cluster or ESX level.

Right-click the virtual Machine -> Fault Tolerance -> Turn on Fault Tolerance

How does the FT enabled virtual machine will be differentiated with non FT VM’s in vSphere client?

FT Enabled Virtual machine will appear in Dark Blue colour as compared to non-protected virtual machines.

By default, Only Primary virtual machine will appear under the cluster and ESX host. To take a look at the secondary VM , Go to Virtual Machines tab of the Cluster or Host.

How Does VMware Fault Tolerance Work?

When you enable Fault Tolerance for the virtual machine, a secondary virtual machine will be created to work with the primary virtual machine in which you have enabled FT. The primary and secondary virtual machine resides on a different ESX hosts in the cluster. Whatever the events or actions performed  by the primary VM will be transmitted via gigabit Ethernet network to be replayed by the secondary virtual machine using VLockstep technology. Eventhough both the primary and secondary virtual machines appear as a single entity  and access a common disk, both  running with the single IP address, MAc address but writes are only performed by the primary virtual machine.The primary and secondary virtual machines sends heartbeat  between each other frequently with millisecond intervals to the check for the availability. If either of the virtual machine loses the heartbeat, other virtual machine will take over the  primary virtual machine role immediately.

What happens when you enabled Fault Tolerance for your virtual machine?

When you enable Fault Tolerance for the virtual machine, a secondary virtual machine (live shadow image of the primary) will be created to work with the primary virtual machine in which you have enabled FT.  The primary and secondary virtual machine resides on a different ESX hosts in the cluster.

What will happen when the ESX host of primary VM failed?

When a failure is detected on the primary VM’s ESX host, the secondary virtual machine which is running on the another ESX server in the same cluster will takes the place of the first one with the least possible interruption of service.

If vCenter is down, will the FT work?
vCenter server is only required to enable FT on the virtual machine.once it is configured, vCenter is not required to be in online for FT to work. FT failover between primary and secondary will occure even if the vCenter is down.

How does Vmware FT differs from VMware HA?

1.VMware HA is enabled per cluster basis but FT is enabled per VM basis.

2. In case of ESX host failure, virtual machines in the  failed host are restarted and powered-on on  the other active hosts in HA cluster. So the restart duration of the virtual machine is the downtime for the virtual machine in HA cluster. But in FT enabled virtual machine, there is no downtime. In case of host failure, secondary VM will become primary and  continuing the execution from the exact point where the primary VM is left off or failed. It happens automatically without data loss, without downtime and with a little delay. Users will not see any interruption.

How do you see the summary status of the FT enabled virtual machines in the ESX host from vsphere client?

Click on Summary tab of the ESX host -> Fault tolerance information and VM counts will be displayed

If you are looking for more VMware interview questions Please take look at  Interview Questions.

All the best and Thanks for Reading!!!!