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VMWare, 2 VM's and a hypervisor

Posted on 2013-05-17
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Last Modified: 2013-05-17
I have a 16 core machine

I have 2 VM's, with each core assigned eight cores.  So no cores are available for a hypervisor

So which does the hypervisor reside since it does not have any cores assigned to it

... or more specifically, which of the 2 VM's will the hypervisor drain resources from, and how can I tell which VM it is currently draining resources from

Thanks
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Question by:Los Angeles1
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by:coolsport00
ID: 39174531
First of all, depending on the VM & that app that is running inside of it, you shouldn't allocate more than 1 or typically at most TWO vCPUs to a VM. A VM utilizes resources of the Host it resides on. There really isn't a way to tell what specific Host CPU and/or Core the VM utilizes as that is controlled by the VKernel CPU Scheduler.

Regards,
~coolsport00
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by:Rsilva98
ID: 39174569
Hi,

First you need to monitor your environment to check who consumes what (cpu, memory etc)

You can use a free tool to gather that data, In my case i use Veeam One Free edition (you can get it here to collect and troubleshoot my environment. Maybe you can remove some cores from the VMs to your hypervisor since is to much for a VM also not the best practices to go for.

Also you can check the users articles like the one hanccocka wrote  HOW TO:  Performance Monitor vSphere 4.x or 5.0.
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coolsport00 earned 500 total points
ID: 39174706
Ok...I turned your question around a little bit, but most of my last comment is accurate. You are wanting to know how an ESXi Host can get CPU resources when you've allocated all cores to all VMs on the Host? Well, that is the beauty of virtualization - OVERCOMMITMENT! :) So, to start off, chances are pretty good that those 2 VMs are NOT going to be utilizing 8 Cores continuously, if at all even 1 core. When a VM is NOT using resources it is assigned, other objects can use those idle resources, up until when the VM that is allocated those resources needs them. And that is the job of the VMkernel CPU Scheduler...to distribute CPU resources where they are needed.

~coolsport00
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by:asavener
ID: 39174802
I have 2 VM's, with each core assigned eight cores.  So no cores are available for a hypervisor
This statement is incorrect.

The hypervisor schedules time on the CPUs, and it will always schedule time for itself.

Since all vCPUs have to be scheduled at the same time, you are likely running into a scheduling bottleneck.  When the hypervisor is using CPU, only one of your VMs can be scheduled for CPU as well.  Bascially, you will always have seven idle cores.

Reduce the number of vCPUs on your VMs.  Unless you're in a lab setting where you're testing high performance computing, it's unlikely that you really need eight vCPUs.  If you do need eight vCPUs, then you need at least two hosts.
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