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Enthusiast
Enthusiast

Reducing vCPU Question...

We have a 2008 Server VM that was a P2V.  It had 4 cores on the physical machine, so that's what it has on the VM now.

Are there any issues with reducing the number of vCPUs to 2?

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5 Replies
rickardnobel
Champion
Champion

There should be no problems with this action on Windows 2008.

My VMware blog: www.rickardnobel.se
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chaikeong
Contributor
Contributor

No issue since it is from multi(4) to multi(2) processors.

It only gets a little tricky when it is from multi to single. (http://www.calazan.com/how-to-change-from-acpi-multiprocessor-hal-back-to-acpi-uniprocessor-hal-in-w...) The link is for windows 2003 but it should work too for windows 2008.

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Cyberfed27
Hot Shot
Hot Shot

No issues as others have stated. Server 2008 is pretty awesome at dealing with hardware changes.

We recently converted a phyiscal box that had 8 cores running on an AMD processor to a VM running on Intel and 2 cores.

Server 2008 took it like a champ.

I've heard of possible instability issues by messing with the # of processors or cores on machines, but I guess I have been lucky we have never seen any ill effects of messing with vCPU's on both Windows 2003/2008. I have even tried "breaking" test VM's by changing the settings to anything you can think of over and over. Never had an issue.

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RParker
Immortal
Immortal

chaikeong wrote:

No issue since it is from multi(4) to multi(2) processors.

It only gets a little tricky when it is from multi to single. (http://www.calazan.com/how-to-change-from-acpi-multiprocessor-hal-back-to-acpi-uniprocessor-hal-in-w...) The link is for windows 2003 but it should work too for windows 2008.

That no longer applies for Windows 2008.  2008 uses the same hal for ALL procs, regardless if it's just 1 or 64.

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shishir08
Hot Shot
Hot Shot

Reducing the number of vCPUs is generally a safe operation, but this strongly depends of the guest O.S., which will actually need to cope with the (virtual) hardware change. Recent Windows and Linux systems usually don't have any trouble with this. FYI - fewer cores are much easier for the Hypervisor to schedule

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