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AnothR
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"If a virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs."

Author : Ivanka Radkova

URL : http:////docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.vm_admin.doc/GUID-285BB774-CE69-44...

Topic Name : Enable CPU Hot Add

Publication Name : vSphere Virtual Machine Administration

Product/Version : VMware vSphere/6.7

Question :

"If a virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs. To change the number of virtual CPUs beyond that limit, you must first power off the virtual machine. By contrast, if a virtual machine already has more than 128 virtual CPUs, you can use hot adding to further increase the number of virtual CPUs to up to 256." Is this sentence right?  I tested this on a running VM with 4 CPUs and hot add enabled.And the CPU number could be increased.

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pragg12
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Hi,

I will try to put in my 2 cents as I am reading this.

If a virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs. To change the number of virtual CPUs beyond that limit, you must first power off the virtual machine. By contrast, if a virtual machine already has more than 128 virtual CPUs, you can use hot adding to further increase the number of virtual CPUs to up to 256.

When I read this for the first time, words "further increase" and "beyond that limit" means that if a VM has CPUs less than 128 and I need to increase CPUs over 128; this requires VM to be powered off. If you want to increase CPU to a number below 128 and if hot add is already enabled, VM does not require to be powered off. Now if a VM already has 128 CPU and is powered ON, there is no problem with further increasing CPU.

Consider marking this response as "Correct" or "Helpful" if you think my response helped you in any way.

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6 Replies
scott28tt
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I‘ve only ever done hot add on small VMs, I think the truth is the opposite of what that document says.


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T180985
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The way i am reading it is if the VM has 128 vCPU or less you cannot add more vCPUs that would take it above 128vCPU without first powering it off. Its not very clear though

Please mark helpful or correct if my answer resolved your issue. How to post effectively on VMTN https://communities.vmware.com/people/daphnissov/blog/2018/12/05/how-to-ask-for-help-on-tech-forums
scott28tt
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I would agree with your interpretation, and that the document is not clear.


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sjesse
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If you look at older documentation, and assume it hasn't changed, the article is misleading

VMware vSphere 5.1

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pragg12
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Hi,

I will try to put in my 2 cents as I am reading this.

If a virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs. To change the number of virtual CPUs beyond that limit, you must first power off the virtual machine. By contrast, if a virtual machine already has more than 128 virtual CPUs, you can use hot adding to further increase the number of virtual CPUs to up to 256.

When I read this for the first time, words "further increase" and "beyond that limit" means that if a VM has CPUs less than 128 and I need to increase CPUs over 128; this requires VM to be powered off. If you want to increase CPU to a number below 128 and if hot add is already enabled, VM does not require to be powered off. Now if a VM already has 128 CPU and is powered ON, there is no problem with further increasing CPU.

Consider marking this response as "Correct" or "Helpful" if you think my response helped you in any way.
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AnothR
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Hi,

I am not a native english speaker.Thank you for helping me to understand!

     If a VM was powered on with hot add enabled, and the current vCPU ≤ 128: To change the number of vCPUs > 128, power off is required.

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