For processors of the same family but of different generations, we can
add them all to the same cluster, leveling the instructions to the
lowest common denominator (limiting the instructions to the older
generation). This way, every node on the cluster has the same set of
instructions. If we do not level the instructions, a migration from an
older generation to a new generation will not cause problems, as the new
generation contains the older generation's set of instructions; the
opposite might cause problems, as the older generation might not have
all the instructions the new generation have.
> So you recommend to make a cluster for each CPU Type ?
It is a common recommendation in the academy; I found an older paper
from VMware [1] that can help you understand this topic; however, if you
dig a bit more you may find other papers.
> Can you define the migration peer for hosts? For example having them
all one cluster but define somehow that migration should be done between
hosts of same CPU?
That would be the idea by segregating hosts in clusters. Could you give
details about your use case of having hosts with different specs (CPU
families) in the same cluster?
Best regards,
Daniel Salvador (gutoveronezi)
[1]
https://www.vmware.com/techpapers/2007/vmware-vmotion-and-cpu-compatibility-1022.html
On 10/04/2024 12:48, R A wrote:
Hi,
is it also problematic migrating to different CPUs of same Family? For example
from Epyc 9654 to Epyc 9754 ?
So you recommend to make a cluster for each CPU Type ? Can you define the
migration peer for hosts? For example having them all one cluster but define
somehow that migration should be done between hosts of same CPU?
BR
-----Original Message-----
From: Guto Veronezi <[email protected]>
Sent: Mittwoch, 10. April 2024 00:14
To: [email protected]
Subject: Re: CPU compatibility
Hello Steve,
For CloudStack, it does not matter if you have hosts with different processors;
however, this is a recommendation regarding how virtualization systems work;
therefore, this discussion happens aside from CloudStack.
When we are dealing with different processors, we are dealing with different
flags, instructions, clocks, and so on. For processors of the same family, but
of different generations, we can level the instructions to the lowest common
denominator (limit the instructions to the older generation); however, it
starts to get tricky when we are dealing with different families. For instance,
if you deploy a guest VM in a host with Xeon Silver and try to migrate it to a
Xeon Gold, the OS of your guest, which already knows the Xeon Silver
instructions, might not adapt to the instructions of the new host (Xeon Gold).
Therefore, in these cases, you will face problems in the guest VM.
If you are aware of the differences between the processors and that mixing
different types can cause problems, then you can create a cluster mixing them;
however, it is not recommended.
For KVM, the parameter is defined in ACS; on the other hand, for XenServer and
VMware this kind of setup is done in the cluster in XenServer or vCenter.
It is also important to bear in mind that, even though you level the
instruction sets between the different processors in the host operating system,
you might still suffer some issues due to clock differences when you migrate a
VM from a faster CPU to a slower CPU and vice versa.
Best regards,
Daniel Salvador (gutoveronezi)
On 09/04/2024 18:58, Wei ZHOU wrote:
Hi,
You can use a custom cpu model which is supported by both cpu processors.
Please refer to
https://docs.cloudstack.apache.org/en/latest/installguide/hypervisor/k
vm.html#configure-cpu-model-for-kvm-guest-optional
-Wei
On Tuesday, April 9, 2024, S.Fuller <[email protected]> wrote:
The Cloudstack Install Guide has the following statement - "All hosts
within a cluster must be homogenous. The CPUs must be of the same
type, count, and feature flags"
Obviously this means we can't mix Intel and AMD CPUs within the same
cluster. However, for a cluster with Intel CPUs, how much if any
leeway is there within this statement? If I have two 20 Core Xeon
Silver 4316 CPUs on one host and two 20 Core Xeon Silver 4416 CPUs
in another, is that close enough? I'm looking to add capacity to an
existing cluster, and am trying to figure out how "picky" Cloudstack is about
this.
Steve Fuller
[email protected]
