Adding a new host with a higher-generation CPU to an existing EVC cluster and migrating running virtual machines

Products

• VMware vSphere ESXi

Issue/Introduction

When expanding a vSphere cluster, administrators may need to add a new ESXi host equipped with a newer or higher-generation CPU than the CPUs of the existing cluster members.
It is often unclear whether the new host can be added directly to a cluster that is already running virtual machines and has Enhanced vMotion Compatibility (EVC) enabled, and whether running virtual machines can be migrated (vMotion) to the newly added host without downtime.

Environment

 

• vSphere environment with an existing EVC-enabled cluster

• A new ESXi host using a CPU generation that is equal to or higher than the EVC baseline of the cluster

• All hosts must use CPUs from the same vendor family (for example, all Intel or all AMD)

• vCenter Server managing the cluster and hosts

 

Resolution

Quick Summary

• A new ESXi host can be added to an existing EVC-enabled cluster as long as its CPU is from the same vendor family and meets or exceeds the cluster’s EVC baseline.
• Once added, running VMs can be migrated (vMotion) to the new host without downtime

Detailed Steps and Considerations

1. Compatibility Requirements

   • CPU Vendor Consistency: All hosts in an EVC cluster must use CPUs from the same vendor family (e.g., Intel-only or AMD-only). EVC cannot mask differences between Intel and AMD processors.

   • EVC Baseline: The CPU of the new host must support at least the same EVC baseline that is configured on the cluster.

   • Ensure that the new host’s BIOS and microcode are updated to the latest vendor-supported level to expose the correct instruction set.

2. Adding the Host

   • Place the new ESXi host in maintenance mode.

   • Add the host to the existing EVC cluster through vCenter Server.

   • EVC masks any CPU instructions that are newer than the cluster baseline, allowing the host to join even if it contains a more advanced CPU generation.

3. Migrating Running Virtual Machines

   • Because EVC ensures all hosts present the same baseline CPU features to the virtual machines, running VMs on existing hosts can be migrated (vMotion) to the new host without downtime.

   • No changes are required on the running VMs. They will continue to operate using the cluster’s EVC baseline feature set after migration.

4. Additional Considerations

   • New CPU-specific features that are above the EVC baseline will remain hidden from virtual machines until the EVC mode is raised and all hosts support the higher baseline.

   • If the new host already contains powered-on VMs, power them off or evacuate them before adding the host to the cluster.