VMware FT vs VMware HA

Knowing your environment uptime and data recovery needs for each server is a key to determine whether you need HA or FT or none of them.

Fault Tolerance

FT creates a full sync copy of your virtual machine on two different ESXi hosts to maximize uptime. In other words, in FT you face two separate virtual machines that are exactly mirrored and disaster recovery takes place in milliseconds as the secondary machine takes over rapidly but FT sucks up your CPU and storage as you keep two sync copy of a particular running vm.  

FT instantly moves virtual machines to a new ESXi host via vLockstep, which keeps a mirrored virtual machine synchronized with the primary vm and ready to take over in less than a second. If your company can not withstand few seconds downtime for end users, you should definitely use FT. 

In addition to zero downtime, in FT you don't lose the in-memory application state in the event of a failure. 

Note: When FT is configured for a vm, vCenter Server need not be online for Fault Tolerance to work and failover occurs from main virtual machine to its mirrored virtual machine.

High Availability

In High Availability (HA) you have just one virtual machine managing by an ESXi host. If the ESXi host fails, the 2nd ESXi takes the roll of vm management.

It might take some seconds or minutes for the vm to boot up. Utilization-wise it would be a better solution as the vm has no mirrored copy to consume your resources like CPU, memory, network and storage. 


So in one sentence: An FT environment has no service interruption but a significantly higher cost, while an HA environment has a minimal service interruption.