You can enable vSphere Fault Tolerance for your virtual machines to ensure business continuity with higher levels of availability and data protection than is offered by vSphere HA.
Fault Tolerance is built on the ESXi host platform (using the VMware vLockstep technology), and it provides continuous availability by having identical virtual machines run in virtual lockstep on separate hosts.
To obtain the optimal results from Fault Tolerance you should be familiar with how it works, how to enable it for your cluster and virtual machines, and the best practices for its usage.
You might encounter error messages when trying to use Fault Tolerance. For information on error messages related to Fault Tolerance, see the VMware knowledge base article at http://kb.vmware.com/kb/1033634.