What is VMware Fault Tolerance and when should I use it?
VMware Fault Tolerance (FT) is a high availability feature that provides zero downtime protection for virtual machines by maintaining an identical secondary VM that runs in lockstep with the primary VM. You should use VMware FT when your applications require continuous availability and cannot tolerate even brief interruptions, such as mission-critical databases, financial trading systems, or regulatory compliance workloads.
Understanding VMware Fault Tolerance basics
VMware Fault Tolerance represents a significant advancement in virtual machine availability technology. Unlike traditional backup solutions that restore systems after failures occur, VMware FT provides continuous protection by maintaining a live, synchronised copy of your virtual machine on a separate physical host.
This approach differs fundamentally from standard high availability solutions. While conventional HA systems restart failed VMs on different hosts (causing brief downtime), fault tolerance technology ensures your applications never experience interruption. The secondary VM takes over instantly when hardware failures occur, maintaining all active connections and in-memory data.
Businesses implementing VMware FT gain protection against complete host failures, hardware malfunctions, and hypervisor crashes. This level of protection becomes particularly valuable for applications where even seconds of downtime can result in significant financial losses or compliance violations.
What is VMware Fault Tolerance and how does it work?
VMware FT creates an exact replica of your primary virtual machine on a different physical host, with both VMs executing identical instructions simultaneously through lockstep synchronisation. The primary VM handles all input/output operations while the secondary VM receives copies of all CPU instructions and memory changes.
The technology operates through VMware's proprietary vLockstep protocol, which captures the primary VM's execution at the CPU level and replays it on the secondary VM. This process ensures both machines maintain identical execution states at all times. Network traffic, disk operations, and user inputs are processed only by the primary VM, while the secondary VM receives deterministic replay information.
When the primary VM experiences a failure, the secondary VM immediately assumes control without requiring a restart or losing any data. This seamless failover happens so quickly that active network connections remain intact, and users typically cannot detect the transition.
When should you use VMware Fault Tolerance?
VMware FT provides the most value for mission-critical applications that cannot tolerate any downtime or data loss. Consider implementing FT when your workloads fall into specific categories that demand continuous availability.
Financial trading platforms, real-time manufacturing control systems, and emergency response applications represent ideal candidates for VMware fault tolerance technology. These systems require instant responsiveness and cannot afford the brief interruptions that traditional high availability solutions might cause.
Regulatory compliance requirements also drive FT adoption. Industries such as healthcare, finance, and telecommunications often mandate specific uptime guarantees that only continuous availability solutions can meet. Additionally, applications with long-running transactions or those maintaining critical in-memory state benefit significantly from FT protection.
However, consider your cost-benefit ratio carefully. VMware FT doubles your compute resource requirements, making it suitable primarily for your most important workloads rather than general-purpose applications.
What are the requirements and limitations of VMware FT?
Implementing VMware Fault Tolerance requires specific hardware and software configurations. Your environment must include compatible Intel or AMD processors with hardware virtualisation support, shared storage accessible by both hosts, and VMware vSphere Enterprise Plus licensing.
| Requirement Category | Specifications |
|---|---|
| CPU Support | Intel VT-x or AMD-V with EPT/NPT |
| Network Configuration | Dedicated FT logging network (minimum 1 Gbps) |
| Storage | Shared storage (FC, iSCSI, or NFS) |
| vSphere Licensing | Enterprise Plus edition required |
Current limitations include CPU constraints (maximum 4 vCPUs per protected VM), limited guest operating system support, and restrictions on certain VM features. You cannot use FT with VMs that have snapshots, linked clones, or certain advanced features like vGPU or device passthrough.
Network bandwidth becomes important for FT logging traffic between hosts. Plan for adequate network capacity to handle the continuous synchronisation data without affecting other network operations.
How do you set up and configure VMware Fault Tolerance?
Setting up VMware FT involves several prerequisite checks and configuration steps. Begin by verifying that your hosts meet all hardware and software requirements, then configure the dedicated FT logging network between your ESXi hosts.
The configuration process follows these steps:
- Verify VM compatibility and remove any unsupported features
- Configure FT logging network with adequate bandwidth
- Enable FT on the virtual machine through vSphere Client
- Select the destination host for the secondary VM
- Monitor the initial synchronisation process
During setup, ensure your shared storage provides sufficient performance for both VMs. Configure your FT logging network on a dedicated VLAN to prevent interference with other network traffic. Monitor the FT status regularly through vSphere Client to verify proper operation and address any warnings promptly.
Test your FT configuration by simulating host failures in a controlled environment. This validation ensures the failover process works correctly and helps you understand the recovery behaviour for your specific applications.
Key takeaways for implementing VMware Fault Tolerance
VMware Fault Tolerance offers unmatched protection for your most important applications, but requires careful consideration of costs and technical requirements. The technology works best for specific use cases where zero downtime is non-negotiable and the additional resource costs are justified.
Evaluate alternatives such as VMware High Availability or application-level clustering for workloads that can tolerate brief interruptions. These solutions often provide adequate protection at lower costs for less critical applications.
Cloud providers can help optimise your fault tolerance strategy by offering managed VMware environments with pre-configured FT capabilities. This approach reduces the complexity of implementing and maintaining fault tolerance while providing access to enterprise-grade infrastructure. At Falconcloud, we provide VMware cloud solutions that can support your high availability requirements, allowing you to focus on your applications while we handle the underlying infrastructure complexity.
