The following checklist contains cluster, host, and virtual machine requirements that you need to be aware of before using vSphere Fault Tolerance.
Review this list before setting up Fault Tolerance.
The failover of fault tolerant virtual machines is independent of vCenter Server, but you must use vCenter Server to set up your Fault Tolerance clusters.
Cluster Requirements for Fault Tolerance
You must meet the following cluster requirements before you use Fault Tolerance.
Fault Tolerance logging and VMotion networking configured. See Configure Networking for Host Machines in the vSphere Client.
vSphere HA cluster created and enabled. See Creating and Configuring a vSphere HA Cluster. vSphere HA must be enabled before you can power on fault tolerant virtual machines or add a host to a cluster that already supports fault tolerant virtual machines.
Host Requirements for Fault Tolerance
You must meet the following host requirements before you use Fault Tolerance.
Hosts must use supported processors.
Hosts must be licensed for Fault Tolerance.
Hosts must be certified for Fault Tolerance. See http://www.vmware.com/resources/compatibility/search.php and select Search by Fault Tolerant Compatible Sets to determine if your hosts are certified.
The configuration for each host must have Hardware Virtualization (HV) enabled in the BIOS.
VMware recommends that the hosts you use to support FT VMs have their BIOS power management settings turned to "Maximum performance" or "OS-managed performance".
To confirm the compatibility of the hosts in the cluster to support Fault Tolerance, you can also run profile compliance checks as described in Create Cluster and Check Compliance in the vSphere Client.
Virtual Machine Requirements for Fault Tolerance
You must meet the following virtual machine requirements before you use Fault Tolerance.
No unsupported devices attached to the virtual machine. See the vSphere Availability publication for more information on Fault Tolerance Interoperability.
Incompatible features must not be running with the fault tolerant virtual machines. See the vSphere Availability publication for more information on Fault Tolerance Interoperability.
Virtual machine files must be stored on shared storage. Acceptable shared storage solutions include Fibre Channel, (hardware and software) iSCSI, NFS, and NAS.
Other Configuration Recommendations
You should also observe the following guidelines when configuring Fault Tolerance.
If you are using NFS to access shared storage, use dedicated NAS hardware with at least a 1Gbit NIC to obtain the network performance required for Fault Tolerance to work properly.
The memory reservation of a fault tolerant virtual machine is set to the VM's memory size when Fault Tolerance is turned on. Ensure that a resource pool containing fault tolerant VMs has memory resources above the memory size of the virtual machines. Without this excess in the resource pool, there might not be any memory available to use as overhead memory.
Use a maximum of 16 virtual disks per fault tolerant virtual machine.
To ensure redundancy and maximum Fault Tolerance protection, you should have a minimum of three hosts in the cluster. In a failover situation, this provides a host that can accommodate the new Secondary VM that is created.