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 or improved with Enhanced vMotion Compatibility. 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. Both Primary VMs and Secondary VMs count toward this limit. The default value is 4.
- das.maxftvcpusperhost
- The maximum number of vCPUs aggregated across all fault tolerant VMs on a host. vCPUs from both Primary VMs and Secondary VMs count toward this limit. The default value is 8.
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 4 vCPUs
