njd62495
Contributor
Contributor

Question about H.E.C and the balloon driver

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My first question is if you have a physical machine that is a dual-core single socket machine (hyperthreading is not enabled), can you have a VM with 4 VCPU's?

My next question is about the balloon driver.

If the limit and reservation of memory are equal and the balloon driver needs to reclaim memory how much memory will the balloon driver reclaim if any at all since the reservation and limit are equal to the allocated memory?

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weinstein5
Immortal
Immortal

The answer to your first question is no - you 4 phyical cores for a quad vCPU VM - and best practice would have at least two quad core chips -

As long as the VM is using all of its memory the balloon driver will not come into play -

If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful

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weinstein5
Immortal
Immortal

The answer to your first question is no - you 4 phyical cores for a quad vCPU VM - and best practice would have at least two quad core chips -

As long as the VM is using all of its memory the balloon driver will not come into play -

If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful

View solution in original post

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RussH
Enthusiast
Enthusiast

Hello.

A dual core single socket processor = max 2vCPU's per VM.

The balloon driver within a VM with limit and reservation set the same would never be used since the VM already has a reservation for all its RAM - ESX cant touch it.

jhanekom
Virtuoso
Virtuoso

The answer to the first question would be no. The maximum number of vCPUs a VM can have must be equal or less than the number of physical cores available. Having said that, it is generally recommended that you allocate as few as possible vCPUs for best performance, preferably not more than half the number of cores available. http://www.vmware.com/pdf/vi_performance_tuning.pdf

I'm going to take a guess at the balloon question... I'd guess you'd be right in that it wouldn't try to reclaim any memory. Out of curiosity: any particular reason you'd want to set the reservation equal to the limit, or is this purely theoretical? (As per the resource management guide, limits and reservations are generally best avoided. My view is that, if anything, it's generally best to use shares.)

njd62495
Contributor
Contributor

Thanks for the repsonses.

Makes things alot clearer now.

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Ken_Cline
Champion
Champion

The answer to your second question is not overly simple...see this thread for details. Scroll down to find posts from kitcolbert and I.

Ken Cline

Technical Director, Virtualization

Wells Landers

VMware Communities User Moderator

Ken Cline VMware vExpert 2009 VMware Communities User Moderator Blogging at: http://KensVirtualReality.wordpress.com/
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njd62495
Contributor
Contributor

Thanks Ken. Good thread. We typically dont over allocate memory on host servers or set the reservation to equal the limit. I was asking the question just for general knowledge and to understand things a little bit better. You never know when someone will ask THAT question 🐵

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