Saturday 2 July 2016

Back to Basics - Part 10 Fault Tolerance

In our couple of blog post related to Back to Basics Series we discussed about Virtual Machine Files (Part1), Standard Switches (Part2), vCenter Server (Part 3),Templates (Part4) vApp (Part 5), Migration (Part 6),Cloning (Part 7), Host Profiles (Part 8), Virtual Volumes AKA VVOL's (Part 9) and we also discussed about the various tasks related to building Home Lab Part1Part 2Part 3,Part 4 and Part 5.

So here we are back again with another back to basics series in which will be focussing on Fault Tolerance another important feature in vSphere and must say one of the cool feature that you will come across.

10 Things You Need to Know !

  1. Fault Tolerance ensures zero downtime for your mission critical applications by providing Instantaneous Failover with Zero Data Loss and no Loss of TCP Connections.
  2. Fault Tolerance Supports Virtual Machine Configured with upto 4 Virtual Cpu and 64 GB Memory.
  3. Fault Tolerance works with vSphere DRS when EVC is enabled and HA is required to enable Fault Tolerance.
  4. Fault Tolerance Virtual Machine can be in any of the disks Formats (Thin, Thick Lazy and Thick Eager Zeroed).
  5. The minute we enabled FT the protected VM is known as Primary and a Secondary copy of that VM is created on another ESXi host which can takeover the Primary VM in case of failure.
  6. Primary Virtual Machine is Continuously Checkpointed and and the checkpoint copies are sent to the Secondary Virtual Machine.
  7. Changes that takes place on Primary are not processed on the Secondary only the Memory is updated on Secondary Virtual Machine over FT network.
  8. FT has shared files (shared.vmft which prevents UUID change and .ftgeneration to avoid split brain conditions) residing on a shared datastore.
  9. When FT is Switched On You cannot modify MemoryReservationShareslimit, Virtual CPU on that Virtual Machine.
  10. When FT is ON vCenter Resets the Virtual Machine Memory Limit and set's the Memory Reservation to the Memory size of the Virtual Machine.

For More Information Refer VMware Documentation 


  1. Replies
    1. All the input to Primary Virtual Machine is Processed at Primary Virtual Machine only the Results are being updated to Secondary Virtual Machine over FT network.