Rafi_abj
Contributor
Contributor

ESX: Dual Core CPU on guest VM Machine - recognized as 2 CPU's?

Hi,

We wish to implement an ESX solution on our organization.

We want the ESX will be on Server with 2 dual core CPU's.

When installing new virtual machine on this kind of server, does the oprating sysytem will recognize 4 CPU's? (2 For each dual core CPU)? ?

Also - are the cores -Dedicated- to that virtual machine? which means that other virtual machine sitting on the same ESX server will not be able toi

use them , when both of the mahcines work at the same time?

I'm asking that because when I use VMWARE server on an HW of 2 Dual core CPU, at the guest virtual machine, one that I configured to use 2 CPU's- I see only 2 cpu's.

(Instead on the real server that the OS see 4 CPU)

Can you please help?

Thank you,

Rafi Abarjeel

Siano Mobile Silicon

it@siano-ms.com

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3 Replies
ejward
Expert
Expert

Hi,

We wish to implement an ESX solution on our

organization.

We want the ESX will be on Server with 2 dual core

CPU's.

When installing new virtual machine on this kind of

server, does the oprating sysytem will recognize 4

CPU's? (2 For each dual core CPU)? ?

When you set up the VM, you can tell it how many CPUs you want. With 2 dual-core physical CPUs in the host ESX server, you can give the VM up to 4 CPUs.

Also - are the cores -Dedicated- to that virtual

machine? which means that other virtual machine

sitting on the same ESX server will not be able toi

use them , when both of the mahcines work at the same

time?

You can also set this, although I never have. You can set a VM to run on specific physical CPUs if you want. That VM can have exclusive rights to that CPU if you want.

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ejward
Expert
Expert

One other thing. Having multiple virtual CPUs in a VM does not always the performance increase you would get if you added a second CPU to a physical machine. in some cases, performance could go down.

With a single virtual CPU, a thread needs to wait for ANY of the 4 physical CPUs in your system to become available before it can process the thread. With 2 virtual CPUs in a VM, the VM must wait for 2 physical CPUs to become available AT THE SAME TIME before it can process the threads. With 4 virtual CPUs, ALL of the physical CPUs in your host server must be available at the same time before the VM can process anything. At that point, why even have a virtual machine?

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bggb29
Expert
Expert

virtual cpu's are independent of the physical cpu.

As stated above esx will be able to present 4 cpus to your virtual guest 2 dual core cpus= 4 virtual cpus.

The hypervisor will mask the underlying hardware.

aas the previuous reply first present 1 vcpu and add another only if needed. Multiple vcpus need to wait for 2 free cpu's to provide a guest cpu time.

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