VM Migration Series – HCX vMotion and EVC

One of the primary benefits of HCX is to be able to leverage HCX vMotion and Replication Assisted vMotion (RAV) for live migrations without lowering the Enhanced vMotion Compatibility (EVC) Cluster Baseline at the destination environment. You can execute the migrations as is without lowering the EVC baseline to Ivy Bridge at the target (lowering the overall available capabilities).

https://kb.vmware.com/s/article/1003212

I just want to take a moment and dive deeper into what this means once you’re executing the HCX vMotion and RAV migrations.

Lets use as an example, a migration from a vSphere 5.5 environment that has Ivy Bridge clusters to a vSphere 6.7 environment with Skylake clusters.



In this scenario, the following behaviors apply:

  • Old to New (Forward Migration)
    A virtual machine created in the 5.5/Ivy Bridge environment can be “forward vMotion migrated” to the 6.7/Skylake environment without lowering the EVC baseline at the destination:
    • HCX by default prioritizes bi-directional migration for virtual machines being migrated.
    • HCX injects Per-VM EVC cpu masks in the .VMX file for bidirectional mobility (this is distinct from the vSphere per-VM EVC feature).
  • Old to New, then back to Old (Reverse Migration)
    A virtual machine created in the 5.5/Ivy Bridge environment that was first “forward migrated” to the skylake environment can be live migrated back to the original environment.
    • The virtual machine can be be reverse migrated even when it has been power cycled at the destination.
    • The HCX injected per-VM EVC cpu masking remains in place during HCX vMotion and RAV reverse migrations.
    • Reverse HCX Bulk Migration clears any existing per-VM EVC cpu masking.
  • Old to New (Forward Migration with Per-VM EVC Disabled in Extended Options)
    • Checking the Disable Per VM EVC extended option deprioritizes bi-directional mobility.
    • HCX does not inject per-VM EVC cpu masks. The virtual machine can use new CPU features after it has been power-cycled.
    • Reverse migration with HCX vMotion and RAV migration will fail.
    • Reverse migration with HCX Bulk migration will work.
  • New to Old (Forward Migration for VM created in the new environment)
    • HCX vMotion and RAV migration to an older environment will fail without EVC.
    • Bulk migration will work.

Thanks for reading!


Gabe

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