Today while teaching a VMware Fast Track course a student asked which guest operating systems that actually supported memory hotadd and cpu hotplug.
This is a great question! Lets dive into some background information.
The ability to use these two features depends on three things:
- Does your VMware vSphere license allow it?
- Does your guest operating system support it?
- Did you enable these two features in your VM?
First of all memory hotadd/CPU hotplug are included in VMware vSphere Enterprise and up.
VMware has previously published a vSphere 5 Cheat Sheet where we can see this:
Secondly we need to make sure our guest operating system supports these features.
I have reviewed some of the typical Microsoft Windows Server versions used from this document:
Microsoft Windows Server 2003: Hotadd Memory
Microsoft Windows Server 2008: Hotadd Memory
Microsoft Windows Server 2008 R2: Hotadd Memory & Hotplug CPU
Microsoft Windows Server 2012: Hotadd Memory & Hotplug CPU
Microsoft Windows Server 2012 R2: Hotadd Memory & Hotplug CPU
Red Hat Enterprise Linux 6.4 Server: Hotadd Memory & Hotplug CPU
Testing by other bloggers seem to conclude some guest OS needs reboot before it works.
Thirdly to actually hotadd memory and/or hotplug CPU we first need to enable it for the VM.
You can ONLY change these settings while the VM is powered off.
The question may then arise, should I leave this enabled by default in our VM templates?
In short, there is an overhead when you enable this and you should only enable it for critical VMs that does not easily tolerate downtime.
Hopefully this should keep you covered. I would however recommend you perform your own testing before you start hotadding and hotplugging.
Remember you could always clone a VM, disconnect the clones network and then see how the clone behaves when you start using these features.
If this helped you then PLEASE leave a comment 🙂
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