Fault Tolerence 

What is VMware Fault Tolerance?

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 ESXi 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?

1. VMware FT is available after versions of vSphere Advanced version (Advanced, Enterprise, Enterprise Plus)

2.Hardware Virtualization should be enabled in the BIOS

3.CPU should be compatible with FT. Please refer VMware site for supported processors.

4.FT enabled virtual machines should be placed in Shared storage (FC,ISCSI or NFS)

5. FT virtual machines should be placed in HA enabled cluster

6. FT cannot be used with DRS in vsphere 4.0 but FT is fully now integrated with DRS from vSphere 4.1

7. In vsphere 4.0, primary and secondary ESX should have same ESX version and patch level. This   limitation is no more from vSphere 4.1. The primary and secondary ESX need not be at same build and
patch level because FT has its own version associated with it.

8. Only 4 FT protetcted virtual machines is allowed per ESX/ESXi host.

9. vMotion and FT Logging should be enabled in vmkernel portgroup of the virtual machine (Separate NIC for vMotion & FT logging is recommeneded along with NIC teaming)

10. Host certificate checking should be enabled (enabled by default)

11. Dedicated 10 GB ethrenet card between ESX servers will give best performance results.

12.  FT ports 8100, 8200 (Outgoing TCP, incoming and outgoing UDP) must be open if any firewall exist between ESX hosts

13. Minimum of 3 hosts in HA enabled cluster is  the requirement for running FT protected virtual machines but 2 hosts is the strong requirement.

14. FT virtual Machines cannot be backed up using the backup technology like (VCB, vmware data recovery),which uses snapshot feature.

15. NPIV (N-PortID Virtualization) is not supported with vmware FT

16. USe Redundancy at all layers(like NIC teaming, multiple network switches, and storage multipathing) to fully utilize the FT features.

17. MSCS clustering is not supported with VMware Fault Tolerance.

18. In vSphere 4.0, Manual vmotion is allowed but automatic load balance using vmotion by DRS is fully supported from vSphere 4.1

19. We cannot use storage vmotion (SVmotion) to migrate FT protected virtual machines from one datastore to another.

20. EVC (enhanced vmotion compatibility) should be enabled in DRS cluster to utilize the automatic load balancing feature provided by DRS for the FT protected virtual machine.

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


1. FT protected virtual machine should be running on the supported Guest operating system

2. FT protected virtual machine’s guest operating system and processor combination must be supported by Fault Tolerance. Please refer VMware Site for Supported Guest OS and CPU combination

3.Physical RDM is not supported for FT protected virtual machines but virtual mode RDM is supported

4.FT protected virtual machine should have eagerzeroed Thick disks. Virtual machine with  thin provisioned disk will be automatically converted to thick disk, while enabling FT for the virtual machine. Make sure enough free space is avaialble in the datastore for this operation.

5.SMP (symmetric multiprocessing) is not supported. Only 1 VCPU per virtual mahcine is allowed.

6.Only 64 GB of  maximum RAM is allowed for the FT VM’s.

7.Hot add and remove devices are not allowed for FT protected VM’s.

8.NPIV is not supported for FT VM’s.

9.USB Passthough and VMDirectPath should not be enabled for FT VM’s and it is not supported.

10. USB and Sound devices are not supported for FT VM’s.

11.Virtual Machine snapshot is not supported for FT protected VM’s.FT virtual Machines cannot be backed up using the backup technology like (VCB, vmware data recovery),which uses snapshot feature.

12. Virtual machine hardware version should be 7 and above

13.Paravirtualized Guest OS and paravirtualized scsi adapter for FT protected virtual machine is not supported.

14.Windows Guest OS should not be using MSCS (Microsoft Cluster services) to Protect the Virtual Machine using FT.

15.FT Protected virtual machines should not be HA disbaled by Virtual Machine level HA settings.

16. FT protected virtual machines cannot be migrated using svmotion. If want to migrate FT protected virtual  machine, disable the FT on the VM, Migrate the VM using svmotion and re-enable the FT.

17. IPv6 is not supported by VMware HA so, it is not supported for FT.

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.

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