Fundamental VM Question

Kato · 06-03-2012, 09:32 AM

If I allocate memory and CPUs to the virtual machine I create, does that mean that I am effectively taking away memory and CPUs from the base machine?
Is this only when the virtual machine is opened and running, correct?
If I do not open the virtual machine, then the base machine should have 100% capacity of the memory and CPUs, correct? Or is this an allocation that will forever take away my resources?

camorri · 06-03-2012, 09:42 AM

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If I allocate memory and CPUs to the virtual machine I create, does that mean that I am effectively taking away memory and CPUs from the base machine?

Yes, you take away memory. CPU? not sure on that. Since the host system really executes the guest system, I would say no.

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Is this only when the virtual machine is opened and running, correct?

Yes. Think of the guest system as an application to the host system. So if any application is not running, no resources are used, other than disk space to store the guest system.

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If I do not open the virtual machine, then the base machine should have 100% capacity of the memory and CPUs, correct?

True.

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Or is this an allocation that will forever take away my resources?

Other than the disk space, the guest system does not use system resources if it is not running.

jefro · 06-03-2012, 04:12 PM

Really can't be answered without a more exact vm and more exact details. VM's is a very generic term for a range of ways to run an OS. The host support also is part of this question.

Depends on the VM. Some do fully remove the ram while others manage it a bit to a lot. Ram also includes swap on some vm's so it may not be an issue.

Normally on boot of a VM the ram is at least marked to be used. It should return to the host when the vm is stopped. Sometimes it doesn't but it should return. It also depends on the VM used.