As with every release VMware increased the version of the virtual hardware of its virtual machines.
Each ESXi / vCenter has a only a limited set of vHW compatibility (e.g. vHW11 MUST run on ESXi6.0++ and therefore managed by a vCenter 6.0++. Check the VMware solution interoperability Matrix for that) and multiple virtual machine related feature enhancements (e.g. new OS-support, new device-support, more vCPU, more vRAM, more more more).
‘vNUMA aware hot-add RAM’
In my job people often ask me.
‘Do I need to upgrade my virtual machine hardware version?’
and I respond with a typical consultant/trainer answer
‘It depends! ;-)’
You need the following questions to answer
Q1. What is the current and the oldest version of vSphere where your VMs might run in a worst-case (failover, recovery, etc.)?
A1. Make sure you are able to run the VMs in all environments (Check the compatibility upwards (newest version) and downwards (oldest version)). You don’t want to start to deal with a vCenter converter to downgrade vHW again.
Q2. Do you need the additional features offered by the specific vHW?
A2. For most use-cases I have dealt with so far, it was not necessary to upgrade the Hardware Version for the new features, except you have pretty BIG MONSTER VMS or the customer had VMs with a vHW < 7. With vHW11 a new feature might come in handy if you are dealing with … I don’t know how to call them… ‘a little bit smaller business critical MONSTER VMs (> 8vCPUs)’.
vSphere 6.0 and vHW11 resolves 1 out of 2 constraints still not everyone is aware about regarding (v)NUMA. vNUMA offers the non-unified memory characteristics of the Server to the guest operating system inside a virtual machine. The guest operating system can now schedule more efficient its processes to the vCPU. This is only relevant by default if you have > 8 vCPUs and multiple Sockets defined as your virtual machine hardware (Mathias Ewald wrote an excellent article about it a while ago).
NEW: If you enable memory-hot add to a VM (to increase the memory size during the runtime – ideal for performance baseline definitions OR quick responses to increasing demand) the additional memory will be extended equally over all existing NUMA nodes of the VM if you are on vHW11.
Unfortunately the other constraint still remains in vSphere 6.0. If you enable CPU hot-add in your VM, the vNUMA characteristic will be hidden from the Guest-OS (KB – 2040375).
Make sure you are aware of the hot-plug settings you have done in your environment with your business critical VMs, since it might have a performance impact (Sample here).
If you want to have memory hot add available including vNUMA support and your complete environment is running on vSphere 6.0, upgrade to vHW11 enable memory-hotplug and disable cpu-hotplug.