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Number of CPU In Windows Hyper-V guest

Posted on 2010-11-24
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Last Modified: 2013-11-06
If I give the guest OS 2 Logical processors , will it be faster than if I give it 1 Logical processor ?
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Question by:soffcec
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16 Comments
 
LVL 8

Accepted Solution

by:
jimmyray7 earned 63 total points
ID: 34208817
Only if your applications can take advantage of multiple processors.  In general, I recommend one vCPU unless you have a reason to add more.
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Author Comment

by:soffcec
ID: 34208842
I am running Exchange 2003 as guest on 1 CPU , the host server (win2008 R2) has 4 CPU.
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LVL 96

Assisted Solution

by:Lee W, MVP
Lee W, MVP earned 63 total points
ID: 34208849
Marginally.  It depends somewhat on what you do.  But windows uses about 40-50 base processes to run the system.  Most are idle and doing nothing 99.9% of the time, but under some circumstances, it may be that you would find the system faster with two CPUs instead of one.  

The one exception to this is if you run a program that is multithreaded - which means it knows how to do things (or more) at once, by itself.  Unfortunately, many products today ARE NOT multithreaded.  Some, like SQL server are, but office, at least through 2007 version is not, for example.
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LVL 17

Assisted Solution

by:OriNetworks
OriNetworks earned 63 total points
ID: 34208943
I havent heard any downsides of adding multiple processors just beware of licensing constraints for example some SQL installations are licensed based on processors.
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LVL 42

Assisted Solution

by:kevinhsieh
kevinhsieh earned 124 total points
ID: 34209184
If your Windows 2003 Exchange 2003 VM is CPU bound (ie. CPU is task manager stays above 50%), then adding an additional vCPU may help. If you don't see the additional processor in task manager after you boot after making the change, you will need to reinstall the Hyper-V Integration compnents.
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Author Comment

by:soffcec
ID: 34209280
When I try to install the integration services the computer asks me to reboot again and again and never finish the setup. Screenshot
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LVL 42

Assisted Solution

by:kevinhsieh
kevinhsieh earned 124 total points
ID: 34209293
You may need to uninstall the integration services completely, and then reinstall them.
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Author Comment

by:soffcec
ID: 34239915
Somehowe , I am not able to see if the integration service is doing anything.
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LVL 5

Expert Comment

by:twcadmin
ID: 34277978
Please clarify your last statement so we can assist.
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Author Comment

by:soffcec
ID: 34279096
When I try to install the  integration service , I get the following messages,
First I get this message

 1Then I get this message
 2At the end I get this message
 3After reboot , the computer goes through the same loop again and again.

There is no integration service installed on the computer, so I can not uninstall it.
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LVL 5

Assisted Solution

by:twcadmin
twcadmin earned 62 total points
ID: 34279584
did it uninstall successfully first as kevinhsieh mentioned?
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Author Comment

by:soffcec
ID: 34279701
I could not uninstall. There was nothing to uninstall.
The installation never worked. I have tried this on 3 other Windows 2003 servers , with no luck. All these servers was running on they own Intel and Intel Xeon machine before I turned them into virtual PC.
I did put up new image of XP as virtual machine for testing and I had none problem installing integration services on it. I am going to run Repair on this virtual image. Maybe it will change the HAL
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LVL 39

Assisted Solution

by:Philip Elder
Philip Elder earned 125 total points
ID: 34390109
What service pack level is Win2K3 at? The VM OS will need the latest service pack before the Integration Services will take.

On the vCPU question:

http://www.microsoft.com/windowsserver2008/en/us/hyperv-supported-guest-os.aspx

A grid with the number of supported vCPUs based on OS version.

Philip
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LVL 39

Assisted Solution

by:Philip Elder
Philip Elder earned 125 total points
ID: 34390123
And to answer your question specifically:

1 vCPU means that the VM OS can only process 1 thread at a time. So, if there are any high CPU usage tasks running in Exchange then there would be very little left over for the OS to use elsewhere.

If the guest OS is Windows Server 2003 with the latest service pack then you can run 2 vCPUs. This gives the OS the ability to dedicate one of those vCPUs to Exchange tasks or other needs while the second vCPU would be used to keep background tasks and the like running. This is a loose analogy without getting into the actual processing.

Having 2 vCPUs always makes things a lot more efficient for a multi-threaded OS such as Windows.

Philip
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