VM Migration Series: HCX & VM Hardware

Virtual Machine Hardware Version matters when it comes to VM migrations whether that be a legacy standalone vSphere running very old many-times-upgraded VMs, a VMware Cloud Foundation deployment, or vSphere Based Hyperscalers & Public Clouds. Depending on the scenario, there are some considerations.

What do we mean by “Virtual Machine Hardware”?

From the Virtual Machine admin guide:

VMware provides devices, resources, profiles, and vServices that you can configure or add to your virtual machine. Not all hardware devices are available to every virtual machine. The host that the virtual machine runs on and the guest operating system must support devices that you add or configurations that you make.”

vSphere Virtual Machine
Why does Virtual Machine Hardware matter for HCX?

Let’s consider one example.

  • Virtual servers running 128GB of video memory are migrated from vSphere 6.5 to vSphere 7 Update 2. In vSphere 6.5, Hardware Version 13 is limited to 128GB. At the migration destination environment, vSphere 7 U2’s HW version 19 allows up to 256GB of video memory. If this is the primary resource for the virtual server, it may be advantageous to upgrade the virtual hardware as part of the migration.
    • This can be a very tangible advantage in preparing the workload for an upgrade to 256GB of video memory.
    • In contrast, this HW version upgrade prevents a reverse migration of the virtual machine.
  • In the inverse scenario, a virtual machine with 256GB of video memory could not be migrated to the 6.5 vSphere environment. In our multi-cloud world, where cloud services are not always in lock-step, this needs to be considered.

Like this examples, there are a variety of scenarios to consider, and in some of these scenarios where VM HW can significantly impact the feasibility of a migration.

What does HCX minimally require?
  • For HCX Bulk Migration operations, a virtual machine must be running at least Hardware Version 7 (this is the ESXi 4.x version)
  • For HCX vMotion, Replication Assisted vMotion (RAV) and Cold Migration, Hardware Version 9 is required (this is the ESXi 5.1 version).
  • For OS Assisted Migration, the source virtual machines do not have an applicable Virtual Hardware version, but they will be created using the latest Hardware Version available in the destination environment.
How does HCX handle VM Hardware during migration?
  • The default mode is to keep the virtual hardware version the same during the migration. This default mode is ideal for bi-directional mobility.
  • When the destination supports newer virtual machine hardware, the Upgrade Virtual Hardware setting in the migration Extended Options can be used to tackle the Virtual Hardware as part of the migration process.
Extended Options
  • The Upgrade Virtual Hardware option is behaves differently by the migration types:
    • HCX vMotion and Replication Assisted vMotion are live operations, the VMs at the destination will become flagged for Virtual Hardware Upgrade on the next reboot.
    • HCX Bulk Migrations will immediately use the newer virtual hardware version at the destination.
    • This mode is ideal when permanently evacuating a source environment, or when adopting a capability that requires higher Hardware Version support is a priority requirement, but
  • HCX does not support migrations to destination environments where the source virtual machine’s current Hardware Version is not supported.
    • Migration to newer infrastructure is what is historically the most typical scenario, but in the world of multi-cloud, where the virtual machine administrators are managing parallel cloud offerings, it is entirely possible to encounter this scenario.
    • In greenfield cloud-to-cloud projects where HCX provides workload mobility, and any to any mobility is a requirement, a baseline hardware version should be established.
    • In scenarios where the HCX defaults are used for migrations from older vSphere to newer vSphere (with newer HW versions available), virtual machines created in the newer vSphere environments cannot be migrated to the older environment.
Additional Considerations?
  • Generally speaking HCX 4 supports the common range of Hardware Versions: 7 – 17.
  • HCX 4.1 is required for migrations to (or from) vSphere 7 Update 1 (HW version 18) & vSphere 7 Update 2 (HW version 19)
  • HCX 4.2.1 is required for migrations to (or from) vSphere 7 Update 3. Although there is no new HW version change with vSphere 7 Update 3.

May the good Lord bless y’all.


Related resources:

Virtual Machine Hardware Versions | VMware KB 1003746

Unable to vMotion vMotion VMs with Hardware Version 8

Virtual machines must be configured with virtual machine hardware version 7 or higher. vSphere Replication FAQ

Downgrading the virtual machine hardware version in ESXi

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