Needless to say, this limitation turned out to be a show stopper since current operating systems and applications require significantly more compute resources. In fact, prior to vSphere 6.0, FT could only be enabled on VMs configured with a maximum of 1 vCPU and 1GB of RAM. The reason for this is due to FT’s lack of support for symmetric multiprocessing and VMs sporting more that 1GB of RAM. In the opening paragraph, I used to word seldom to indicate that FT has been generally overlooked at least until vSphere 6 came along. It does not provide any application level protection meaning that manual intervention is still required if a VM experiences OS and/or application failures. That said, keep in mind that FT protects only at a host level. On-Demand FT protects business critical VMs and the corresponding business processes such as payroll applications and payroll runs against data loss and service interruption. Since FT is a resource expensive process, you may decide to employ scripting to enable and disable FT on a schedule just to mention one way of doing it. Occasionally, you may come across the term On-Demand Fault Tolerance. FT is also useful in scenarios where expensive clustering solutions are impractical or costly to implement.

FT bolsters business continuity by mitigating against data loss and application downtime, something that an HA cluster on its own cannot completely deliver.

For this reason, a 3-host cluster is the recommended minimum even though FT works just as well on clusters with just 2 nodes.įigure 1 – FT architecture (Source: The one benefit that immediately stands out, is that Fault Tolerance raises the High Availability bar one notch higher. Similarly, if the secondary VM’s ESXi host goes offline, a secondary VM is created on yet another host, assuming one is available. In the event that the primary VM ‘s host fails, the secondary VM will take over immediately with zero interruption and downtime. VMware Fault Tolerance (FT) is a process where a virtual machine, called the primary VM, replicates changes to a secondary VM created on an ESXi host other than the one hosting the primary vm. In today’s post, I’ll go over the new features introduced in vSphere 6.0 and how to enable FT on your VMs. If you’ve read my post on High Availability, you probably know that Fault Tolerance is a feature intrinsic to an HA enabled cluster. Fault Tolerance is a seldom used feature even though it’s been available since the days of VMware Infrastructure, the old name for what today is known as VMware vSphere the software suite comprising vCenter Server and the ESXi hypervisor along with the various APIs, tools, and clients that complement it.

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