komanek
Enthusiast
Enthusiast

ESXi hardware replacement (possible transition from Intel to AMD CPU)

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Hello,

in my organization we are running vSphere Enterprise Plus clusters on relatively old hardware (ESXi hosts with Intel Xeon E5-2640 v4 CPU). We are planning to purchase new host servers to replace the old ones. Our guests base is pretty heterogenous, many Linux distros and Windows servers of different versions, also various virtual hardware versions. At the beginning, I thought, the new hosts could be either Intel or AMD based (with the cost of the downtime for the cold migration in the case of Intel to AMD transition), but then I read an article 

https://kb.vmware.com/s/article/1011788

Now I am afraid there could be some VMs, nowadays smoothly running on Intel CPU, which will not work on AMD based hosts. Is there a way to check our environment and to rule out (or to confirm) problems of this type to be expected? 

As a university financed from the public budget we are obliged to do a competitive tendering, so it could be a problem to request Intel CPUs only, as it'd be perceived as a possible vendor discrimination.

Thanks in advance for your thoughts.

Regards,

  David

 

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Tibmeister
Expert
Expert

Linux, and Windows, will switch out the kernel as needed based on the architecture.  While both AMD and Intel are x86, there are CPU features (extensions) that are different, and both OS kernels are intelligent enough to switch in and out.  This is also why it's very important to check the Compatibility matrix for ESXi version to CPU to Guest OS to EVC mode.  If you run a new OS on a version of ESXi that is not fully supported, on a brand new CPU, there could be issues.  This is part of the reason why VMware began removing support for certain CPU models, to prevent these odd situations from occurring and causing problems.  Microsoft even removes support for certain CPU's from time to time for the same reason, to prevent BSOD's and other issues.

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Tibmeister
Expert
Expert

The Windows guests should be running a generic HAL, so will adapt easily.  I've not had any issues with Windows boxes moving between AMD and Intel (from former to later).  Linux, no issues there either.

The only thing is that from Intel to AMD is a Cold Migration only, so you will take an outage.  Same is true if you do not have EVC enabled on your existing cluster and you put new Intel hosts in there, it will not work.

komanek
Enthusiast
Enthusiast

Thanks for the reply. I also thought so, but in the cited article, VMware states otherwise:

... many distributions of Linux choose a kernel that is optimized for the specific processor on which it is being installed ...

... Linux virtual machine created on a host might not work when you migrate it to a host with a significantly different processor, e.g. from a host with Intel processor to a host with AMD processor, a host with AMD processor to a host with Intel processor, or even between hosts with different generations of processors from the same vendor if EVC is not used.
This problem is not specific to virtual machines and can occur on physical computers. For example, if you move a hard drive with a Linux installation from an AMD machine to an Intel machine, you might experience problems trying to boot from that drive.


It's pretty recent (2021), so I wonder how to tell which kernel is "generic" and wich will fail to start after the cold migration from Intel to AMD host. Since we have many flavors of RH/CentOS/Alma/Rocky, Debian/Ubuntu, SuSe and FreeBSD, all of various versions, some of them have external admins of various degree of experience, it is now of a major concern to me. Hopefully at least VCSA, SRM and NetApp appliances are CPU-type agnostic.

 

 

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stadi13
Hot Shot
Hot Shot

Hi David

you don't have to bother. All your VMs are seeing and using the x86 architecture. This does not depend on Intel or AMD. Your VMs will run smoothly on both cpu types. You have to make sure no VMs is using/talking to any cpu hypervisor extensions like Intel VT. This was the case last year with Citrix Netscaler and has also been resolved in newer version.

Regards

Daniel

komanek
Enthusiast
Enthusiast

Hello,

thank you both for your opinion. I will try not to worry and will see later, what CPU family I will have to use.

D.

 

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hgov
Enthusiast
Enthusiast

Hi,

For many years one of our development environments used a mixture of AMD and Intel ESXi hosts in a cluster. The only issue I ever ran into relating to the differing architectures was that we could not migrate a running vm from one architecture to another. We could only live migrate between hosts with similar vendor CPU's. To move vm's between hosts with different vendor CPU's the vm had to be powered off first. Overall, it shouldn't be an issue - although life is much easier now that all cluster CPU's are from a single vendor.

Thanks.

Henry

Tibmeister
Expert
Expert

Linux, and Windows, will switch out the kernel as needed based on the architecture.  While both AMD and Intel are x86, there are CPU features (extensions) that are different, and both OS kernels are intelligent enough to switch in and out.  This is also why it's very important to check the Compatibility matrix for ESXi version to CPU to Guest OS to EVC mode.  If you run a new OS on a version of ESXi that is not fully supported, on a brand new CPU, there could be issues.  This is part of the reason why VMware began removing support for certain CPU models, to prevent these odd situations from occurring and causing problems.  Microsoft even removes support for certain CPU's from time to time for the same reason, to prevent BSOD's and other issues.

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komanek
Enthusiast
Enthusiast

Thank you all! Although I believe all the answers you gave me, there could be just one of them masrked as "correct" in this forum, I believe. So I am giving it to the most detailed one.
Thanks again.

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