cpu and memory hot add on esxi 5.5?

[llewell_uk]

Could anyone let me know if there is much of an overhead by enabling hot add for cpu and memory on your guest VM's?

[schepp]

Hi,

when enabling Hot-Add, the VM might use the overhead, it would need when you would add the additional number of vCPUs and RAM to that VM.

To get an idea of the possible overhead, look at the documentation: vSphere 5.5 Documentation Center

[vfk]

Just to add, cpu hotplug effectively disable vNUMA, they are mutually exclusive. VMware KB: vNUMA is disabled if VCPU hotplug is enabled

This is something to keep in mind, you might not actually scale to 8vCPU and tweak vNUMA settings, but it should be considered.

[JPM300]

Much to the point @vfk mentioned if your using Hot add it will disable vNUMA which can hurt large VM's using more then 8vCPU or that have been fine tuned to their numa nodes for performance.  A good use case for this is a SQL server.