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Complete vSphere newbie here...

Background:
So, I have a 12 core machine with 24 VMs on it. Currently, all the processing power is shared between these VMs equally.

The question:
Can I configure one VM to be given two CPU's worth processing no matter what's happening on the other machines?

My Research:
I tried two things in vSphere...

  1. I set the reservation and limit on one VM to equal the same as two cores. To test if my objective was being reached, I measured the time it would take to gzip a file when other VMs were running nothing and when other VMs were running CPU intensive operations. I expected the time to gzip the file would be the same because this VM gets priority for some processing. Unfortunately, the time taken to gzip the file when other VMs were running something was significantly more than when other VMs were not running anything.

  2. I tried setting the Hyperthreaded Core Sharing mode to Internal hoping that this would mean that my VM would get at least an entire core to itself. This did not work either.

Thanks in advance!

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2 Answers 2

You can set that machine to have priority over the other machines by setting the shares higher. More info here.

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CPU resource allocation works as followed: 1 virtual socket CPU = a normal share of 1000.

So when you give 2 vCPU, you will have a share of 2000 and that VM will have more priority regarding to the physical host processing than VM with only a share of 1000.

You can trick that configuration on any VM with editing their settings and defining a resource allocation (low, normal, high or even custom) in the Resource tab.

  • Low will give you a share amount equals to 500 x nb vCPU.

  • Normal will give you a share amount equals to 1000 x nb vCPU.

  • High will give you a share amount equals to 2000 x nb vCPU.

  • Custom will give you a share amount equals to what you have typed

It's better to avoid setting VM limitations for that kind of purpose.

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