VMware EVC Mode: The Complete Guide to Enhanced vMotion Compatibility in vSphere Clusters

Ever tried adding a new server to your VMware cluster only to find that vMotion won’t work because the processors don’t match? You’re not alone. This common frustration has a powerful solution: Enhanced vMotion Compatibility (EVC) Mode.

Whether you’re managing a small three-node cluster or a sprawling enterprise environment, understanding EVC mode can save you countless hours of troubleshooting and enable seamless hardware upgrades without expensive downtime.

What is EVC Mode in vSphere?

Enhanced vMotion Compatibility (EVC) is a cluster-level feature in VMware vSphere that enables live migration of virtual machines between ESXi hosts with different CPU generations from the same vendor. Think of it as a translator that ensures all processors in your cluster speak the same language to your virtual machines.

When you enable EVC mode on a vSphere cluster, it establishes a baseline CPU feature set that all hosts must present to virtual machines. Even if you have newer processors with advanced instruction sets, EVC masks those extra features so that VMs see a consistent CPU across all hosts.

Why EVC Mode Matters

The reality of IT infrastructure is that hardware refreshes happen gradually. You purchased five Dell servers with Intel Xeon E5-2600 v3 processors three years ago, and now you need to expand. Those processors are discontinued, and you can only buy newer Xeon Gold or Platinum series. Without EVC, those VMs won’t migrate between your old and new hosts.

EVC mode solves this by creating a uniform CPU environment across mixed-generation hardware, enabling:

• Live migration (vMotion) between hosts with different processor generations
• Hardware lifecycle extension by mixing old and new servers in the same cluster
• Zero-downtime maintenance when adding new nodes or performing upgrades
• Simplified cluster expansion without replacing existing infrastructure
• Cost savings by avoiding forklift upgrades

How VMware EVC Mode Works

At its core, EVC operates through CPU instruction set masking. Here’s what happens behind the scenes:

The CPUID Mechanism

Every processor has a CPUID—essentially an API that tells the system what instructions the CPU can execute. When a virtual machine boots, it queries the host’s CPUID to understand available CPU features like SSE4.2, AVX, or AVX-512.

EVC intercepts this communication and enforces a standardized CPUID baseline across the entire cluster. The vSphere hypervisor already abstracts the physical CPU from virtual machines, and EVC leverages this abstraction to control which CPU features are exposed.

Baseline Selection

When configuring EVC, you select a baseline corresponding to a specific processor generation:

• Intel Baselines: Merom, Penryn, Nehalem, Westmere, Sandy Bridge, Ivy Bridge, Haswell, Broadwell, Skylake, Cascade Lake, Ice Lake, and newer
• AMD Baselines: AMD Opteron Generation 1-4, EPYC, and newer generations

The baseline you choose determines which CPU instructions are available to VMs. If you select “Intel Haswell,” for example, all hosts—whether they have Haswell, Broadwell, Skylake, or Cascade Lake processors—will only expose Haswell-level instructions to virtual machines.

Important Requirements

• All processors must be from the same vendor (Intel or AMD—no mixing)
• Intel VT-x or AMD-V must be enabled in BIOS/UEFI
• All hosts must support the selected EVC baseline
• vCenter Server version must support your processor generations

Types of EVC: Cluster-Level vs Per-VM EVC

VMware introduced two ways to implement EVC, each with distinct advantages.

Cluster-Level EVC (Traditional)

Cluster-level EVC applies the baseline to all ESXi hosts in the cluster. Every VM running in that cluster inherits the cluster’s EVC mode. This is the original implementation and remains the most common approach.

Advantages:

• Simple to configure and manage
• Ensures uniform compatibility across the entire cluster
• Best for homogeneous workload environments

Limitations:

• All VMs are bound to the same baseline
• Cannot have different baselines for different workloads
• Changing the baseline requires VM power cycles in some scenarios

Per-VM EVC (Introduced in vSphere 6.7)

Per-VM EVC makes the EVC mode an attribute of the virtual machine itself rather than the cluster. Available for VM hardware version 14 and higher, this provides granular control.

Advantages:

• Different VMs can have different EVC baselines
• EVC configuration travels with the VM during migrations
• Greater flexibility in heterogeneous environments
• Enables workload-specific CPU requirements

Limitations:

• VM must be powered off to change per-VM EVC baseline
• VM cannot power on if its baseline exceeds host capabilities
• More complex to manage at scale

The per-VM EVC configuration is stored in the VM’s VMX file with entries like:

featMask.vm.cpuid.Intel = "Val:1"
featMask.vm.cpuid.FAMILY = "Val:6"
featMask.vm.cpuid.MODEL = "Val:0x4f"

How to Enable EVC Mode in vSphere: Step-by-Step Guide

Prerequisites Checklist

Before enabling EVC, verify:

1. All ESXi hosts use processors from the same vendor
2. Check VMware Compatibility Guide for supported EVC modes
3. Identify the oldest processor generation in your cluster
4. Ensure Intel VT-x/AMD-V is enabled on all hosts
5. Have vCenter Server credentials with appropriate permissions

Enabling EVC on a New Cluster (Recommended)

VMware recommends enabling EVC when creating a cluster to avoid complications:

1. Log into vSphere Client and navigate to the vCenter inventory
2. Right-click on the Datacenter and select “New Cluster”
3. Name your cluster and configure basic settings
4. Enable EVC by checking “Enable EVC for Intel Hosts” or “Enable EVC for AMD Hosts”
5. Select EVC Mode from the dropdown—choose the baseline matching your oldest CPU
6. Verify compatibility (vCenter shows validation results)
7. Click OK to create the EVC-enabled cluster
8. Add hosts to the cluster—they’ll automatically inherit the EVC mode

Enabling EVC on an Existing Cluster

Enabling EVC on a cluster with running workloads requires more care:

1. Navigate to your cluster in vSphere Client
2. Click the Configure tab → Settings → Configuration → VMware EVC
3. Click Edit to open EVC settings
4. Review the compatibility report—vCenter shows which VMs and hosts are compatible
5. Power off incompatible VMs (VMs running on hosts with CPUs newer than your baseline)
6. Select Enable EVC for Intel or AMD hosts
7. Choose the baseline matching your oldest processor generation
8. Review validation results—ensure “Validation succeeded” appears
9. Click OK to apply

Pro tip: VMs running on the host with the oldest processor can remain powered on if using vCenter 4.1 or later, as their CPU features already match the baseline.

Enabling Per-VM EVC

For virtual machines requiring specific EVC modes:

1. Power off the virtual machine
2. Right-click the VM and select “Edit Settings”
3. Navigate to VM Options → Advanced → VMware EVC
4. Select “Activate” to enable per-VM EVC
5. Choose the CPU baseline from the dropdown
6. Verify that the baseline doesn’t exceed cluster EVC mode (if in an EVC cluster)
7. Click OK to save changes
8. Power on the VM to apply the new EVC configuration

Using VMware Compatibility Guide to Determine EVC Modes

The VMware Compatibility Guide is your definitive resource for EVC planning:

1. Visit the Broadcom Compatibility Guide (formerly VMware Compatibility Guide)
2. Search for your server model or CPU family
3. Select your ESXi version
4. Click CPU/EVC Matrix to see supported baselines
5. Identify the lowest common baseline across all your processors

For example, if you have:

• Host 1: Intel Xeon E5-2600 v3 (Haswell)
• Host 2: Intel Xeon E5-2600 v4 (Broadwell)
• Host 3: Intel Xeon Gold 6100 (Skylake)

Your EVC baseline should be set to Intel Haswell to ensure all three hosts can participate.

Real-World EVC Mode Scenarios

Scenario 1: Gradual Hardware Refresh

Challenge: A financial services company has a 10-node cluster running ESXi hosts with Intel Sandy Bridge processors. They need to add five new hosts with Cascade Lake processors for increased capacity.

Solution: Enable EVC mode at Intel Sandy Bridge baseline. The new Cascade Lake hosts will mask advanced features and present Sandy Bridge-compatible instructions to VMs. This allows seamless vMotion across all 15 hosts while maintaining production uptime.

Scenario 2: Multi-Datacenter VM Mobility

Challenge: An organization wants to migrate VMs between their primary and DR datacenters, which have processors from different generations.

Solution: Implement per-VM EVC on critical VMs with a baseline compatible with both sites. VMs can now migrate between datacenters using Cross-vCenter vMotion while maintaining CPU compatibility.

Scenario 3: Preventing Migration Failures

Challenge: After adding a new host with Ice Lake processors to an existing cluster, VMs cannot migrate to the new host, causing DRS failures.

Solution: Enable cluster-level EVC at the appropriate baseline. After powering off and restarting affected VMs, DRS can now balance workloads across all hosts, including the new Ice Lake system.

Performance Considerations and Best Practices

Does EVC Impact Performance?

A common concern is whether masking CPU features reduces performance. The reality is nuanced:

• EVC itself has zero overhead—it simply controls which instructions are visible
• Most workloads see negligible impact (estimates suggest 99% of workloads are unaffected)
• Performance reduction occurs only if your workload specifically leverages masked advanced instructions
• Compute-intensive applications using AVX-512 or specialized instruction sets may see degradation

Best Practices for EVC Implementation

1. Enable EVC from Day One Configure EVC when creating new clusters, even if all processors currently match. This prevents headaches during future expansions.

2. Choose the Right Baseline

• Set baseline to your oldest processor generation
• Don’t select a baseline older than necessary (no reason to use Penryn if all hosts are Haswell)
• Plan for future hardware purchases when setting baselines

3. Document Your Configuration Maintain clear documentation of:

• Current EVC mode for each cluster
• Processor models in each host
• Rationale for baseline selection
• Migration paths for future hardware

4. Test Before Production

• Enable EVC in a test cluster first
• Verify VM migrations work as expected
• Test application performance with EVC enabled
• Monitor for any unexpected compatibility issues

5. Use Per-VM EVC Strategically Reserve per-VM EVC for specific use cases:

• VMs that need to migrate across different EVC clusters
• Workloads requiring specific CPU features
• Test VMs used for compatibility validation

6. Monitor and Validate

• Use vSphere performance monitoring tools post-enablement
• Watch for DRS migration failures
• Review VM compatibility reports regularly
• Stay current with VMware KB articles on EVC baselines

7. Plan for Baseline Upgrades As older hosts are retired, you can raise the EVC baseline:

• All hosts must support the new higher baseline
• Use the “Change EVC Mode” dialog to check current availability
• Power off VMs and restart to apply new baseline features

Troubleshooting Common EVC Issues

“Host cannot be admitted to cluster’s current EVC mode”

Cause: The host’s processor doesn’t support the cluster’s EVC baseline, or VMs are using CPU features beyond the baseline.

Solution:

• Verify the host processor is compatible using VMware Compatibility Guide
• Ensure all VMs on the host are powered off before adding to cluster
• Check for nested virtualization (VHV) which can cause unexpected EVC mode issues

“Virtual machine failed to power on”

Cause: Per-VM EVC baseline exceeds the cluster’s EVC mode or host capabilities.

Solution:

• Check VM’s EVC configuration (Edit Settings → VM Options → Advanced → VMware EVC)
• Verify the VM’s baseline is equal to or lower than the cluster baseline
• Ensure destination host supports the VM’s required CPU features

vMotion Fails After Disabling EVC

Cause: Hosts revert to their native CPU instruction sets, creating incompatibility.

Solution:

• Re-enable EVC mode on the cluster
• Power off and restart affected VMs to resync CPU features
• Avoid disabling EVC in production environments with mixed hardware

TSX Instructions Causing Compatibility Issues

Cause: Intel disabled TSX in some Haswell processors via microcode, causing them to appear as Ivy Bridge.

Solution:

• Check if your Haswell processors have TSX disabled
• Set EVC mode to Ivy Bridge if necessary
• Update ESXi and microcode to latest versions

EVC Mode vs. Other VMware Features

EVC and vSphere HA

High Availability (HA) is not impacted by EVC changes. When HA fails over a VM, it power-cycles the VM on the new host, allowing it to detect new CPU features naturally.

EVC and vSphere DRS

Distributed Resource Scheduler (DRS) relies heavily on EVC. Without EVC in mixed-hardware clusters, DRS cannot migrate VMs between incompatible hosts, severely limiting its effectiveness.

EVC and Storage vMotion

Storage vMotion works independently of EVC since it only migrates storage, not the running VM state. VMs can be moved between datastores regardless of EVC configuration.

EVC and Fault Tolerance (FT)

Fault Tolerance requires compatible CPUs and benefits significantly from EVC. FT maintains a shadow VM, and EVC ensures both primary and secondary VMs see identical CPU features.

The Future of EVC in Modern vSphere Environments

As virtualization evolves, EVC remains critically relevant:

• Hybrid cloud migrations: EVC enables VM mobility between on-premises and cloud environments with different hardware
• Kubernetes on vSphere: Project Pacific and vSphere with Tanzu benefit from EVC when running containerized workloads across mixed hardware
• AI and ML workloads: Specialized instruction sets (AVX-512, AMX) make EVC baseline selection more critical for performance
• Longer hardware lifecycles: Economic pressures encourage mixed-generation clusters, making EVC essential

Frequently Asked Questions

Can I mix Intel and AMD processors with EVC?
No. EVC requires all processors to be from the same vendor. EVC cannot translate between Intel and AMD instruction sets.

Will enabling EVC slow down my VMs?
For the vast majority of workloads, no. EVC has zero overhead and only affects performance if your applications specifically use masked advanced instructions.

Can I enable EVC without powering off VMs?
Yes, when using vCenter 4.1 or later. VMs on the host with the oldest processor can remain running. VMs on newer hosts may need to be powered off and restarted.

What happens if I add a host with a CPU older than my EVC baseline?
The host cannot join the cluster. You must either lower the EVC baseline (requiring VM power cycles) or upgrade the host’s processor.

Is per-VM EVC better than cluster-level EVC?
Neither is inherently better. Cluster-level EVC is simpler and suitable for most environments. Per-VM EVC provides granular control for complex scenarios with varying VM requirements.

How do I check what EVC mode my VM is using?
In vSphere Client, select the VM → Configure tab → Settings → VM Options → Advanced → VMware EVC. The pane displays the current EVC mode and CPUID details.