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:

  • 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.
    • The same virtual machine can be immediately reverse migrated using HCX vMotion.
    • If the virtual machine is power cycled in the 6.7/Skylake environment, you can no longer reverse migrate it with HCX vMotion (it will fail with CPU compat errors). You can still use HCX Bulk migration in this case for a low-downtime migration. 
  • If a virtual machine created in the 5.5/Ivy Bridge environment and is Bulk migrated to the 6.7/Skylake environment, you cannot reverse HCX vMotion (it will fail due to CPU compat).  You can still use HCX Bulk migration in this case.
  • If a virtual machine is created in the 6.7/Skylake environment, you cannot use HCX to HCX vMotion into the 5.5/Ivy Bridge environment (it will fail due to CPU compat);  You can bulk migrate in this case.
  • If a virtual machine has been bulk migrated many times (e.g. in testing – it can become possible for a 5.5/Ivy Bridge to 6.7/Skylake forward migration to fail. (Will be addressed in a future release, thanks Bilal Ahmed for the report!)


    In general HCX can be used for migrations from older to newer without making changes to the baseline.

There are other variables like Per-VM EVC (In vSphere 6.7), and per VM EVC in the HCX Extended Options. I will come back to cover those another time.

Thanks for reading!


Gabe

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