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Wednesday, 15 December 2010

High Host CPU on Windows 2000 Virtual Machine in vSphere

I had a Windows 2000 Server that I had used a Physical to Virtual migration with the VM Converter tool, the original physical server had two CPUs and when I mgrated I dropped this to one vCPU as the server needed very little resource.

The problem arose that the Windows 2000 Server was consuming a high percentage of the host CPU usage while the VM Guest itself as idling at 0% CPU usage. The problem I found by researching the VMWare KB articles is that the Windows 2000 Server will try to set itself into idle mode when not in use, in a physical server this results in low power consumption, in a virtual server this results in low CPU usage on the host.

However my server was not able to enter idle mode and so was stuck trying to do so and was consuming a high percentage of the host CPU. The issue was that I had not changed the ACPI HAL for the server in Windows 2000 to tell it it was no longer a dual CPU server, I changed this by entering the Device Manager and then expanding the Computer object, below this is the ACPI Multi Processor object.

If you enter the properties of this object you can from the Advanced Tab choose to update the driver, here you choose to select the driver from a list and show all hardware that is compatible. The list will then show the Uni Processor HAL object that can be used.

I added this object and then restarted the server and the CPU use on the host has now reduced to a normal idle level.

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