VMware vSphere FT is a way to improve the availability level for critical VMs, with a (close to) zero-downtime technology. The protected VM is named the primary VM, and for each primary VM, there is a duplicate VM named secondary VM (or sometimes also the shadow VM).
VMware vSphere FT provides continuous availability by having two identical VMs running on separate hosts. The secondary VM execution is identical to that of the primary VM. Primary and secondary VMs are still monitoring each other's status. If primary VM failed, the secondary VM immediately replaces the primary VM.
VMware vSphere FT has also some limits—for each VM, it supports a maximum of 4 vCPU and 64 GB RAM. For each host, it supports a maximum of 4 fault-tolerant VMs. VMware vMotion migration is supported for both VMs, as also the different virtual disk formats and the native backup...
