CPU AND MEMORY HOT PLUG IMPACT?

[VMnoobs1]

Hi,

need to know that if someone has the knowledge of the impact on the VMware if we turn on the CPU and Memory hotplug enabled on all of our VMs?

will it slow it down? does it takes more resources than to have it disabled?

any input is highly appreciated

thanks

[mhampto]

I do not see this causing a performance impact being enabled on all the VM's. 

[jhague]

Answer is 'it depends'! Hot plug and vNUMA are mutually exclusive. vNUMA optimises the scheduling of vCPUs on physical cores, if there are more vCPUs in a VM than exists within a physical CPU socket, vNUMA will make sure they are scheduled in the most efficient way - same goes for memory which is assigned to a 'local' CPU E.g. you have 256GB memory in a 2 CPU socket system then you have 128GB per channel. If you have a VM with more than 128GB it is a wide VM and can benefit from vNUMA.

If you enable hot plug then this will be disabled, if you have smaller VMs you won't notice. If you have larger VMs you may not even notice depending on the utilisation of your environment and what is running on the VMs.

It often comes down to a trade off between what is most important and what is best from an operational perspective too. Also just because the VM supports hot plug does not mean the OS/App does e.g. in the case of certain DB software...

Ps Frank Dennenman explains it a lot better than I can - Impact of CPU Hot Add on NUMA scheduling - frankdenneman.nl