Vmware CPU - how to work out Vcpu per core

Posted on 2012-09-21
Medium Priority
Last Modified: 2012-10-14
I am so confused as to how many machines you can have per core on a esxi host.

For example: I was under the impression that if you have a 4 core Xeon processor with hyperthreading that you would be able to handle 8 VM's (because you have 8 logicial CPU's)? before you would create a round house effect where the vm's would 'que' for CPU access.

The above example i found in a blog - would that be incorrect?

But reading this:

Hancocka is running 48 machines on 4 cores?

Is there something that i am missing?

All we are looking to run on our host is VDI's that are assigned 1vCPU.
Question by:Kenzii

Expert Comment

ID: 38420999
Hello Kenzii,

You can have more vCPUs than physical CPU but that is not best practice in production environment.

More about that on link below

Best Regards,
LVL 15

Accepted Solution

Raj-GT earned 2000 total points
ID: 38421005
VMware and all type 1 hypervisors use scheduling to handle access to physical resources so yes, you can allocate a single CPU core to multiple vCPUs.

you may need to take some care for VDI though, read the blog below for some more information on scheduling for VDI.

LVL 24

Expert Comment

by:Nagendra Pratap Singh
ID: 38421139
VMware and others all use the round house thing.

Most VMs are idle at least for some time and at that moment don't participate in queues etc.

You can have 20 VMs running on a single Xeon box.
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LVL 124
ID: 38421182
not really, because you can have as a rule of thumb 5-6 VMs per physical core.

and this is because of the Hypervisor clever CPU scheduler, which switches CPU cycles/time between VMs.

and as you've quote me, we also run between 80-100 VDI Workstations on a Dell R810 128GB 24 Cores.

This is less than are normal 5-6 VMs, because these are usually servers, that are idle for most of the time, compared to Desktops in use by Students every timetabled hour, which are busier.

Author Comment

ID: 38421260
So this is how we have things setup at the moment:

all servers reside on a seperate box. So idleing will generally occur on this.

Our main box that we are looking to use for VDI boxes. 16GB RAM Xeon E31230 3.20Ghz

4 VDI's on this box with 2GB RAM each and 1vCPU.

Looking into this it appears as soon as we play a video through the VDI that will use flash redirection it hammers all VDI's on the server. But CPU % sits around 25%.

We use quest vWorkspace which provisions the VDI's and then provides the connection.

Our internet line is 100MB down. 10mbs UP. which with 4 machines connecting to the internet does not seem alot.

But sounds like this is not going to a CPU problem after all.
LVL 124
ID: 38421291
Flash does cause High CPU utilisation.

A Dual Processor Server is probably better here, and more RAM in the Host.

Because the scheduler can allocate cores across multiple physical processors, rather than just a single.

Expert Comment

ID: 38421348
Flash player in VDI works slow.

You can find similar questions on the internet.

Look at Flash acceleration :

And VMware View Flash Optimizer plugin

Hope this will help.


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