VMware Fault Tolerance fails to turn on in a two node cluster

Products

• VMware vCenter Server

Issue/Introduction

Running FT protected virtual machines in a two node cluster is supported. Problems can occur when there is a need to vMotion the primary virtual machine from one host to the other. As the primary and secondary virtual machines cannot reside on the same host, FT must be turned off so that the secondary virtual machines is destroyed. The primary virtual machines can then be vMotioned to the other host.

This article provides steps to prevent the monitor mode from changing during a vMotion that causes FT to fail.

Symptoms:

• VMware Fault Tolerance (FT) is configured and functional for virtual machines in a two node cluster.
• FT is turned off so that the primary virtual machine can vMotion to a different host in the cluster.
• Attempts to turn on FT after performing a vMotion fails with errors similar to the following:

The virtual machine is running in a monitor mode that is incompatible for Fault Tolerance.

The Fault Tolerance configuration of the entity VM_name has an issue: The virtual machine's current configuration does not support Fault Tolerance.

Environment

VMware vCenter Server 4.1.x
VMware vCenter Server 4.0.x
VMware vCenter Server 5.0.x

Resolution

This issue occurs if the monitor mode changes during the vMotion process. FT requires the monitor mode be set to Use Intel VT-x/AMD-V for instruction set virtualization and software for MMU virtualization for the monitor mode to not change during the vMotion process.

The default setting for the virtual machine monitor mode is Automatic and FT sets the monitor mode appropriately behind the scenes. If the hosts in the cluster support the Use Intel VT-x/AMD-V for instruction set virtualization and Intel EPT/AMD RVI for MMU virtualization option, the monitor mode is changed to this during the vMotion process.

To set the monitor mode explicitly to Use Intel VT-x/AMD-V for instruction set virtualization and software for MMU virtualization:

Note: In some instances, the virtual machine needs to be powered off in order to change the monitor mode.

1. Right-click the virtual machine in question and choose Edit Settings.
2. In the virtual machine Properties window, click Options and select the CPU/MMU Virtualization option under the Advanced heading.
3. Select the radio button next to Use Intel VT-x/AMD-V for instruction set virtualization and software for MMU virtualization.
4. Click OK.
5. For the setting to take effect, the virtual machine needs to be power cycled or vMotion to another host. When this is complete, FT can be turned on for the virtual machine.