VMWare and CPU - Question

llarava used Ask the Experts™

I have a lab env with a Dell server that has 2 CPUs and 10Gb of RAM and ESX 3.5 install. I have some users connecting and doing some testing, nothig big just some stuff with Microsoft Office and running some other apps but all simple stuff. I have about  between 8 to 10 VMs running all the time and most of the time they are idle and perhaps sometimes I can get between 2 or 4 computers with connected users (so 4 VMs being used an 4 or more up to 6 running but idle).

The performance of those machines sometimes is pretty bad and even the management of the ESX server with VC is also really slow.

I was wondering if the cpu over utilization might be the cause of the issue.

In the current situation we are running 10 virtual machine on a host which has only 2 physical processors.

Because of this only 2 virtual machines can execute their processes on
the physical processor.

Rest of the 8 virtual machine has to wait till the processor is free.

Does that make sense?

Also what should be the recommended physical CPUs if we want to run up to 12 VM's (WXP) ?

Thank you.
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Absolutely! Try poking around with V-Sphere's/ESX's settings. Try to throttle how much of the CPU can be used by the machine. If it really is just basic stuff like running Microsoft Office, then set down the virtual processor speed for each VM to say, 800Mhz. I don't know if ESX has management options for killing (or setting VMs idle) after a certain length of time and bringing them back up when there is demand for them.

Take a look at this VMware knowlegebase article as well ->

Here is a link for an article about monitoring CPU usage -> http://oreilly.com/windows/excerpts/9780596805227/recipe-5-9-monitoring-cpu-usage.html

Best of luck to you!

One thing that I forgot to add. Make sure that the VM's were created cleanly. There shouldn't be a lot running inside of the VM other than the OS and the main applications. Skip out on leaving services running that won't even be used (for instance, no Real player, QuickTime, iTunesHelper). You don't need to show your users that Java needs to be updated. It's a useless message for them, and it does sit there using RAM). Make sure that Windows patches are applied. These are crucial, and can give the VM a slight performance boost).

Hope this helps also.


Thanks for your suggestions. This is a production env. so I feel that we are definetly running shot on the phyisical CPUs. I can go ahead and do some tweaking here and there but I think sooner or later the users will feel the pain.

I wanted to verify that I wasn't the only one that belives that we need to get more CPUs in order ti fix our problem with performance.

Is there any sort of calculator by VMWare or 3rd party vendor that can be used to get aprox the needs of the physical hardware that a server has to have in order to run a certain number of VMs. I understand it will not be exact since the needs are diferents based on server roles, etc. but something that could give me some sort of baseline would be great.

Thanks again.
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Take a look at this article. It was the best I could find. -> http://www.vmware.com/support/esx21/doc/esx21install_requirements2.html

This is about the best calculator I could find. It however is really designed to find out just how many new servers you should implement. Best thing I can think of is checking their specs and seeing how close they match yours. At about step 12, you start inputting your data. You might want to select the select 'New server infrastructure' for a few more options. -> http://advisors.dell.com/AdvisorWeb/Advisor.aspx?advisor=c82c3ec8-c94f-4602-9a41-c20382db1cd0&c=us&l=en&cs=555

If your company can afford it, I'd say to get another server in there. I would generally recommend either Intel's (Xeon) or AMD's (Opteron) quad core CPUs if possible. There really is a performance gain with the multiple cores. If you need to see how a specific server will fit into your current infrastructure, most manufacturers do give you time to evaluate the unit. If it's not quite powerful enough for the business, box it up and ship it back.

Best Regards.



I have ran "esxtop" I have attached the results on a screenshoot. I think the performance looks pretty sluggish specially I am concerned about the %wait time (miliseconds) for accessing the CPU.

What do you think?


I haven't mentioned but it looks pretty obvious...anyway the name of the VMs have been removed basically each line represents a VM that is turned ON.

Sorry for my tardiness. I have looked over the screenshot. Yes, the machine appears to be under heavy load. I would take a close look at machine ID 33 and 22. Both are using large amounts of the VCPU. If you can, try killing those machines for a day or two and seeing how performance is. All of %RDY readings also worry me. None of the machines really should go over 5-6%. If I understand the concept correctly, this is where the VM couldn't actually process instructions due to physical CPU load. The shear amount of VMs appears to be taking quite a toll on the hardware. It might just be about time to upgrade the hardware. Have you considered upgrading to ESXi?

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