VMworld 2008; VMware announced Fault Tolerance (FT) in ESX 4 as a new feature that allows continuous availability for selected virtual machines (VM). FT is a technology that allows continuous availability virtual machines with literally zero downtime and zero data loss, even surviving server failures, while staying completely transparent to the guest software stack.
While it was a great new feature; FT enabled VM’s were not a very common sight in datacenter environments.
FT not being a very common sight in datacenters was mostly due to the restriction of only 1 vCPU per FT virtual machine. This limitation was quite limiting the usability of FT in your datacenter. Most business critical VM’s, that could benefit from FT the most, were in need of multiple vCPU’s in order to meet the performance requirements. Further challenges were the limited options on how to back-up your FT enabled VM’s as creating VMware snapshots was not possible.
Other cluster and host requirements for legacy FT, or UP-FT, were:
- A HA enabled cluster is required.
- Shared storage is required.
- VMDK’s must be eager zeroed thick provisioned.
- Host CPU’s must be VMware FT capable and belong to the same processor model family.
- Ensure that all ESX hosts in the VMware HA cluster have identical ESX versions and patch levels.