Before using vSphere Fault Tolerance (FT), consider the high-level requirements, limits, and licensing that apply to this feature.
Requirements
The following CPU and networking requirements apply to FT.
CPUs that are used in host machines for fault tolerant VMs must be compatible with vSphere vMotion. Also, CPUs that support Hardware MMU virtualization (Intel EPT or AMD RVI) are required. The following CPUs are supported.
- Intel Sandy Bridge or later. Avoton is not supported.
- AMD Bulldozer or later.
Use a 10-Gbit logging network for FT and verify that the network is low latency. A dedicated FT network is highly recommended.
Limits
In a cluster configured to use Fault Tolerance, two limits are enforced independently.
- das.maxftvmsperhost
- The maximum number of fault tolerant VMs allowed on a host in the cluster. The default value is 4. There is no FT VMs per host maximum, you can use larger numbers if the workload performs well in FT VMs. You can disable checking by setting the value to 0.
- das.maxftvcpusperhost
- The maximum number of vCPUs aggregated across all fault tolerant VMs on a host. The default value is 8. There is no FT vCPU per host maximum, you can use larger numbers if the workload performs well. You can disable checking by setting the value to 0.
Licensing
The number of vCPUs supported by a single fault tolerant VM is limited by the level of licensing that you have purchased for vSphere. Fault Tolerance is supported as follows:
- vSphere Standard and Enterprise. Allows up to 2 vCPUs
- vSphere Enterprise Plus. Allows up to 8 vCPUs
