For all who have not seen ESXi4 beta or presentations at VMWorld 2008, VMware announced a new feature called Fault Tollerance (FT). A system with two virtual machines in an active/passive configuration. All instructions that are executed on the active virtual machine are copied over a high speed network to the passive virtual machine. When the active virtual machine fails the passive virtual machine takes over with zero downtime so no service interruption.

This information is based on a ESXi4 beta so there is no guarantee that this feature will appear in the final product.

A demo of this feature can be found here.


  • For now FT will only support uni-processor VM’s.
  • HA/DRS cluster and VMotion.
  • Shared storage.
  • Minimal 1 Gb dedicated network.

Note: there is no extra storage needed for the passive virtual machine. It uses the same virtual hard disks as the active virtual machine on the shared VMFS.

Erik Sloof filmed the FT demo in Vegas, it can be found here.