Changing Number of Guest Processors

[BDorroh]

I need some advice on converting physical machines that have two processors. Normally when the conversion is done, I modify the settings from 2cpu to 1cpu and then power on the VM. But on machines where I've done this in the past, it takes a very long time to get to the security screen. When I look at CPU performance of the VM, the processor is pegged at 100% so I've wound up putting the CPU back to 2 processors. The VMware Preformance Tuning whitepaper says to configure single processor virtual machines with a UP/HAL kernel and multi-procesor virutal machines with a SMP/HAL Kernel. Can someone clarify this for me and maybe point me in the right direction for fixing this problem in my scenario? Thanks! (btw, in this case it's just a base OS, no apps.)

[Chris_S_UK · Accepted solution]

having a mismatch between the HAL and the number of vCPUs leads to issues with CPU utilisation because the VM does not "idle" properly.

All you should need to do is go into Device Manager, under Computer, and change the type to the appropriate version (uniprocessor or multiprocessor) to reflect whether the VM is SMP or not.

[DigitalVoodoo]

Chris' statements above are right on - you need to make sure that your HAL gets changed accordingly. Doing that manually post-conversion has been somewhat spotty in the past as a search of the forums will show, although I believe that has been somewhat addressed with Win2003 SP2. I use PlateSpin's PowerConvert to do my P2Vs for this very reason as they do a good job "downgrading" the HAL on the fly during the conversion process.

[RParker]

You can add processors, but you can't remove processors via the hardware.

What you can do is find a Windows Server disk of the same SP level as the on you want to change the HAL on. You boot from the CD, and immediately following the boot it will give the option to insert the OEM drivers disk (press 'F2'). At this point press 'F5'. After a few moments you will get prompted to change the HAL to ACPI uniprocessor. Select this one, and move on. Go past the first screen (for install) and let it discover the existing OS install, and at this point you can use 'R' to repair it. You won't lose any settings/data but you will have to reinstall patches/SP.

Otherwise that's how you properly change the HAL.

Sometimes plug and pray will let you change from multi to uni, but if it doesn't, the above steps will help.

[BDorroh]

Is it better to power on the VM and change it in Windows before changing the guest OS settings? Or change the guest settings, boot, and then change it in Windows?

I guess I'm trying to avoid that painful length of time it takes Windows to boot when I change the guest OS settings first. I've seen it take 20 minutes minimum in the past...

[RParker]

You have to edit the VM setting first, Windows will see whatever you present. Then change Windows after you set your VM parameters.

[BDorroh]

Thanks for the help. It worked great! No issues so far.