Fault Tolerance
It's fair to say that vSphere HA provides only a basic level of protection; in the event of a host failure, it restarts VMs. vSphere FT, however, provides a higher level of availability and protects VMs from host failure without any downtime, any loss of data, or connection interruptions.
FT can be enabled for any critical VMs. Continuous availability is provided by creating and maintaining a secondary VM that is an exact copy of the primary one. Primary and secondary machines exchange heartbeats. This allows them to monitor each other's status.
If a host where primary VM is running fails, the secondary VM is activated within a few seconds to replace the primary one, and a transparent failover occurs.
To ensure that both VMs are exactly the same, VMware uses the vLockstep technology. vLockstep executes identical sequences of x86 instructions on both the machines. The primary VM replays all the events taking place between the processor and virtual I/O devices back to the secondary...
