Advice : Maximum VCPU

This is for discussing general topics about how to use VirtualBox.
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hdrapin
Posts: 1
Joined: 30. Apr 2010, 14:14
Primary OS: Mac OS X Leopard
VBox Version: PUEL
Guest OSses: Ubuntu

Advice : Maximum VCPU

Post by hdrapin »

Hi,

I have an iMac with a core i7, this is a 4 core with (more) 4 "virtual" CPU. My computer have "virtually" 8 cores.

Question 1 : In VirtualBox (3.1.6) I can use up to 16 VCPU on virtual Machine, does it means that; for all VM, VirtualBox will double the number of physical CPU/Core ?

Question 2 : Starting in version 3.0 the maximum number of VCPU is 32.. does it make sens to have more than 1 or 2 VCPU on virtual machine ?

My understanding is : until we won't be able to dedicated one VPCU to one CPU, the "load" on processor will be split on several CPU, not on only one. So using several VPCU doesn't have benefits ?

What is the best practice regarding the number of VCPU ?

Many thanks
Technologov
Volunteer
Posts: 3342
Joined: 10. May 2007, 16:59
Location: Israel

Re: Advice : Maximum VCPU

Post by Technologov »

>Question 1 : In VirtualBox (3.1.6) I can use up to 16 VCPU on virtual Machine, does it means that; for all VM, VirtualBox will double the number of physical CPU/Core ?

Yes, it means your host cores will be over-committed.

>Question 2 : Starting in version 3.0 the maximum number of VCPU is 32.. does it make sens to have more than 1 or 2 VCPU on virtual machine ?

In some cases, yes (mathematics or server load). In most cases, not (desktop load).

>My understanding is : until we won't be able to dedicated one VPCU to one CPU, the "load" on processor will be split on several CPU, not on only one. So using several VPCU doesn't have benefits ?

The total load of all guest VCPUs will be split among the real CPUs.

>What is the best practice regarding the number of VCPU ?

IMO VCPUs should not exceed logical CPUs on your host.

-Technologov
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