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  • 1.  Migration should require EVC Mode but does not

    Posted Jul 06, 2023 05:24 PM

    We have two existing clusters, one with Intel Haswell and the other with Intel Broadwell processors. We created a new cluster with Intel Ice Lake processors.

    We need to migrate all VMs from the existing clusters to the new one. The VMware Compatibility Guide tells me that on the new cluster I will need to enable EVC Mode for Intel Haswell in order to do so.

    I have not enabled any EVC Mode on the new cluster but VM migrations are working fine with no warnings. Why could this be?

    I don't want to enable EVC Mode if I don't have to, but I'd hate to migrate a bunch of VMs and then something happens where I do need to enable it because then I'd have to power off all of the VMs I've migrated in order to do so.



  • 2.  RE: Migration should require EVC Mode but does not
    Best Answer

    Posted Jul 06, 2023 05:39 PM

    There's no need to activate EVC mode just to be able to migrate VMs. As long as the new CPUs support all the features of the old one, the migration is possible.

    Anyway, there's no drawback in enabling EVC mode with the highest possible mode, that's supported by all hosts in a cluster.
    I always do this to avoid possible compatibility issues in the future, e.g. if hosts with newer CPU models are added.

    André



  • 3.  RE: Migration should require EVC Mode but does not

    Posted Jul 06, 2023 05:54 PM

     wrote:

    There's no need to activate EVC mode just to be able to migrate VMs. As long as the new CPUs support all the features of the old one, the migration is possible.


    Could you expand on that? I thought the whole point of EVC Mode was to enable migration between hosts with different processor generations.

    Does that fact that I'm migrating across different clusters mean anything? Each cluster's hosts all have the same processor generation. Maybe EVC Mode comes into play more when you have hosts with different processor generations in the same cluster?



  • 4.  RE: Migration should require EVC Mode but does not

    Posted Jul 06, 2023 06:07 PM

    >>> Maybe EVC Mode comes into play more when you have hosts with different processor generations in the same cluster?

    Exactly! With EVC you basically define the CPU features which are presented to a VM when it is powered on.
    So if you have hosts with different CPUs, but want to be able to vMotion VMs regardless on which host a VM has originally been powered on, you need to set EVC to the lowest common EVC mode.

    Without EVC being enabled, you can vMotion VMs that have been powered on on older CPUs to hosts with newer CPUs, but not vice-versa.

    André



  • 5.  RE: Migration should require EVC Mode but does not

    Posted Jul 06, 2023 06:11 PM

     wrote:

    Without EVC being enabled, you can vMotion VMs that have been powered on on older CPUs to hosts with newer CPUs, but not vice-versa.

    André


    Ahh that makes sense because when I tried to migrate one back from newer to older I had to power it off first.



  • 6.  RE: Migration should require EVC Mode but does not

    Posted Jul 06, 2023 06:18 PM

    ... and just to add to this.

    A VM that has been powered on an older CPU can be vMotion'd to a newer host, and also be vMotion'd back to the older host, because the CPU feature set remains the same with the VM as long as it's not power cycled (power off/power on).

    André