VMware FT

VMware FT

FT Information


http://www.vmware.com/files/pdf/perf-vsphere-fault_tolerance.pdf - VMware vSphere™ 4 Fault Tolerance: Architecture and Performance

http://www.vmware.com/files/pdf/resources/ft_virtualization_wp.pdf - Protecting Mission-Critical Workloads with VMware Fault Tolerance

http://kb.vmware.com/kb/1010601 - Understanding VMware Fault Tolerance

http://kb.vmware.com/kb/1013428 - VMware Fault Tolerance FAQ


http://www.virtualizationteam.com/virtualization-vmware/vmware-esx-40-ft-fault-tolerant-sneak-peek.h... - VMware ESX 4.0 FT – Fault Tolerant – Sneak Peek

About vLockStep:



Demo of VMware's vSphere Fault Tolerance (FT)


FT requirements


  • Only some CPU can be used: http://kb.vmware.com/kb/1008027 - Processors and guest operating systems that support VMware Fault Tolerance

  • Hardware Virtualization (HV) must be enabled in the BIOS for each host in the cluster (but this is also required for EVC and x64 VMs)

  • The ESX hosts that run the primary and secondary Fault Tolerance nodes, must be running the same build of ESX.

  • All ESX hosts used by VMware Fault Tolerance must be members of a VMware High Availability (HA) cluster. VMware HA must be enabled for VMware Fault Tolerance to function.

  • Networking must be configured properly to ensure proper VMware Fault Tolerance functionality.

  • In some cases the VM must be powered off to enable FT (for some guest type and to convert vmdk from zeroedthick to eagerzeroedthick )

To check compatibility there is also a VMware utility:

Site Survey - http://www.vmware.com/download/shared_utilities.html


FT 1.0 limitations

  • Only 1 vCPU for each VM protected by FT

  • Require compatible CPU (http://kb.vmware.com/kb/1008027)

  • No vmxnet3 support (http://kb.vmware.com/kb/1013757)

  • No snapshot support (and no VCB and other snap-based backup program)

  • No physical RDM ()

  • Do not use both ESX and ESXi hosts in clusters with fault tolerant virtual machines (http://kb.vmware.com/kb/1013637)

  • VM memory will be reserved to the max value

  • Only eagerzeroedthick disks are supported ()

  • Seems that Linux guest with VMI are not supported for FT


FT 1.0 best practices

  • Use dedicated 1Gb (better if is 10Gbs) link for FT logging

  • Use SVMotion to converter from thin to thick, or use dastore browser/inflate (but in this case the VM must be powered off)

  • Use CPU with similar speed

  • Do not use CPU power management

  • With Nehalem CPU, HT could be enable without problem (and is also suggested by VMware)

  • Enable FT with the VM powered off

See also: http://www.vmware.com/files/pdf/fault_tolerance_recommendations_considerations_on_vmw_vsphere4.pdf



FT does not protect against OS or application failures, only from ESX host failures.

See also:



VMware FT vs Marathon eveRun







Enable/Disable FT with script

Could be useful to implement some backup solution on FT protected VM.

Version history
Revision #:
1 of 1
Last update:
‎10-25-2009 03:33 AM
Updated by: