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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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4 Replies
RParker
Immortal
Immortal

"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)? ? "

Yes but you have to configure the VM's to use 2 or 4 vCPU.

"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? "

This is settable, however, you do not not want to dedicate the CPU's to a VM. This is called CPU Affinity, bad. Don't do it.

ESX 3.0 does a good job of giving CPU for VM's that need it, if you specify a CPU for a certain VM, you are limiting the ability of the ESX to handle the load.

"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) "

In the virtual world, you are telling the VM that it THINKS it is a physical box. Then you give that physical machine 1, 2 or 4 CPU. By doing this you are limiting the ability of the machine to only see what you want it to see, so in VM ware, you told it 2 CPU, that's ALL it will get.

VM Ware is limited to ONLY 2 CPU also, with ESX you can give 4, and see ALL CPU. However, you will find that ESX is so efficient, you may not even need 2 CPU, I would start with 2, and test your application performance inside the VM, I am pretty sure this will be plenty.

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Rafi_abj
Contributor
Contributor

Hi,

Thank you for the quick response.

A few notes:

The esx is for disaster recovery environment - so I need the guest VM will recognize 4 CPU's (on the host physically there are 2 CPU of 2 cores each).

What I'm asking actually is if I have an HW of 2 CPU, and each has 2 cores, on the ESX can I set 4 CPU's to the guest virtual machine?

The same question is - when configuring new virtual machine - when asked for a number of CPU's - the number represent the physical CPU's? or the total number of cores? (1 CPU of dual core will present an option of 2 CPU's for example).

As I understand from your reply - dedication of CPU is not mandatory - and this is the preferred situaltion with me.

Thank you again, and waiting your final answers....

Rafi

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mikemohr
Contributor
Contributor

The number of CPUs available in the list comes from the number of cores in the host. If you assign 1 vCPU to the VM you will not have access to both cores of the pCPU. If you need 4 vCPUs in the VM you will be giving the VM access to all four cores of the pCPUs.

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RParker
Immortal
Immortal

"What I'm asking actually is if I have an HW of 2 CPU, and each has 2 cores, on the ESX can I set 4 CPU's to the guest virtual machine?"

YES.

"The same question is - when configuring new virtual machine - when asked for a number of CPU's - the number represent the physical CPU's? or the total number of cores? (1 CPU of dual core will present an option of 2 CPU's for example)."

The CPU equate to physical CPU visible to the ESX server. So if you have 2 Dual Core Procs, that is 4 CPU (it doesn't matter to ESX if they are cores or not, its better for performance if they ARE cores).

So the MAX CPU you can set for a guest is 4CPU (this may be limited by a license, and a standard license allows for maxium of 4 CPU).

1 CPU equals 1 vCPU, if you want the guest to "see" 2 CPU, then you need to set to 2vCPU.

In the physical world, a machine can see ALL the processors, in virtual, you give the guest visibily to ONLY what you want it to see. That's the major difference.

Even given your situation, I would START with 2vCPU and test performance. Because of the way ESX schedules time on a CPU (and given that you add more VM/Guest) having each VM with more CPU is more overhead for management of resources (memory AND CPU).

You can always add more later, but you will find 2 vCPU is going to be fine, I can almost guarantee it. ESX is a pure environment. NO vendor related sotware, no serial ports, sound, USB, or other junk to interfere with processing power. ONLY memory, CPU, and a generic SCSI, Video and Network driver. That's It.

Your guest and OS will run WAY more efficient, and the overhead of each core is much less, thereby needing less CPU to manage your guests and their processes.

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