RazaAbbas
Contributor
Contributor

Guest VM Configuration

I'm running an XP VM on ESXi Server version 4. I'm attempting to test a software on different hardware configurations - different VMs with varying CPU speed, memory and hard disk space. While HDD and Memory can be easily configured using vSphere, I was wondering how can I manipulate the CPU speed so as to simulate a slower system. I can see there are "Reservation and Limit" options in Resources tab in VM settings, but my question is whether setting a reservation / limit to a particular value has the same effect as running a slower cpu? For example, If I set Reservation and Limit to 667Mhz ... is it the same as running on a 667Mhz CPU? I need to know this so that I can claim having tested the software on a slower system.

Thanks!

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JoJoGabor
Expert
Expert

If the VM has a single vCPU, you can set a limit which is the maximum number of CPU cysles the VM can use. However if other VMs are sharing the underlying pCPU it may not be accurate. You could do one of two things:

Set reservation to 667Mhz and the limit to 667Mhz (or maybe 668 if this isnt allowed) That way the VM is guaranteed to use that number of recources.

OR

Set processor affinity so that the VM you want to monitor is using a specific pCPU (make usre not to set it to pCPU 0 as the Service COnosle will also use this) Then set the affinity of other VMs to use other pCPUs.

I think the first method is much easier.

RazaAbbas
Contributor
Contributor

Thanks for the quick response.

As it stands, my VM is the only VM on the server. HT is disabled and number of vCPUs is set to 1. However, in VM Settings > Resources tab (Scheduling Affinity), it tells me that the number of Available CPUs is 4 (physical CPUs). Could you please elaborate what that means and if that in anyway would invalidate my claim of having tested on a single-core 667Mhz CPU?

Much appreciated.

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JoJoGabor
Expert
Expert

The Affinity setting allows you to select which physical CPUs to run the VM on. You dont normally need to set this, and remember that the service conosle is just another VM which runs on CPU 0.

If your VM is set to run 1 vCPU it will only run on one physical CPU.

azn2kew
Champion
Champion

Perhaps you would like to know more in depth with Resource Management Guide that would explain everything you need to know.

If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!

Regards,

Stefan Nguyen

VMware vExpert 2009

iGeek Systems Inc.

VMware, Citrix, Microsoft Consultant

If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!! Regards, Stefan Nguyen VMware vExpert 2009 iGeek Systems Inc. VMware vExpert, VCP 3 & 4, VSP, VTSP, CCA, CCEA, CCNA, MCSA, EMCSE, EMCISA
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