Before configuring vSphere Fault Tolerance, you should be aware of the features and products Fault Tolerance cannot interoperate with.

vSphere Features Not Supported with Fault Tolerance

The following vSphere features are not supported for fault tolerant virtual machines.

  • Snapshots. Snapshots must be removed or committed before Fault Tolerance can be enabled on a virtual machine. In addition, it is not possible to take snapshots of virtual machines on which Fault Tolerance is enabled.
  • Storage vMotion. You cannot invoke Storage vMotion for virtual machines with Fault Tolerance turned on. To migrate the storage, you should temporarily turn off Fault Tolerance, and perform the storage vMotion action. When this is complete, you can turn Fault Tolerance back on.
  • Linked clones. You cannot enable Fault Tolerance on a virtual machine that is a linked clone, nor can you create a linked clone from an FT-enabled virtual machine.
  • Virtual Machine Backups. You cannot back up an FT-enabled virtual machine using Storage API for Data Protection, vSphere Data Protection, or similar backup products that require the use of a virtual machine snapshot, as performed by ESXi. To back up a fault tolerant virtual machine in this manner, you must first disable FT, then re-enable FT after performing the backup. Storage array-based snapshots do not affect FT.
  • Virtual SAN.

Features and Devices Incompatible with Fault Tolerance

For a virtual machine to be compatible with Fault Tolerance, the Virtual Machine must not use the following features or devices.

Table 1. Features and Devices Incompatible with Fault Tolerance and Corrective Actions
Incompatible Feature or Device Corrective Action
Symmetric multiprocessor (SMP) virtual machines. Only virtual machines with a single vCPU are compatible with Fault Tolerance. Reconfigure the virtual machine as a single vCPU. Many workloads have good performance configured as a single vCPU.
Physical Raw Disk mapping (RDM). Reconfigure virtual machines with physical RDM-backed virtual devices to use virtual RDMs instead.
CD-ROM or floppy virtual devices backed by a physical or remote device. Remove the CD-ROM or floppy virtual device or reconfigure the backing with an ISO installed on shared storage.
Paravirtualized guests. If paravirtualization is not required, reconfigure the virtual machine without a VMI ROM.
USB and sound devices. Remove these devices from the virtual machine.
N_Port ID Virtualization (NPIV). Disable the NPIV configuration of the virtual machine.
NIC passthrough. This feature is not supported by Fault Tolerance so it must be turned off.
vlance networking drivers. Fault Tolerance does not support virtual machines that are configured with vlance virtual NIC cards. However, vmxnet2, vmxnet3, and e1000 are fully supported.
Virtual disks backed with thin-provisioned storage or thick-provisioned disks that do not have clustering features enabled. When you turn on Fault Tolerance, the conversion to the appropriate disk format is performed by default. You must power off the virtual machine to trigger this conversion.
Hot-plugging devices. The hot plug feature is automatically disabled for fault tolerant virtual machines. To hot plug devices (either adding or removing), you must momentarily turn off Fault Tolerance, perform the hot plug, and then turn on Fault Tolerance.
Note: When using Fault Tolerance, changing the settings of a virtual network card while a virtual machine is running is a hot-plug operation, since it requires "unplugging" the network card and then "plugging" it in again. For example, with a virtual network card for a running virtual machine, if you change the network that the virtual NIC is connected to, FT must be turned off first.
Extended Page Tables/Rapid Virtualization Indexing (EPT/RVI). EPT/RVI is automatically disabled for virtual machines with Fault Tolerance turned on.
Serial or parallel ports Remove these devices from the virtual machine.
IPv6 Use IPv4 addresses with the FT logging NIC.
Video devices that have 3D enabled. Fault Tolerance does not support video devices that have 3D enabled.
Virtual EFI firmware Ensure that the virtual machine is configured to use BIOS firmware before installing the guest operating system.