Enthusiast
Enthusiast

Guest VM sizing - CPU/RAM

I am trying to find a best way to size the VMs, I understand the NUMA concept and ideally VM should stay withing same NUMA domain rather then crossing in between.

If the Blade has 2 sockets x 12 cores, i understand the single NUMA domain would be 12 cores or 12 VCPUs? so VM should not be allocated with more then 12 CPUs in order to stay in the same NUMA domain?

in this example it would have 24 cores in total or 48 Logical CPUs if Hypertreading on, does this mean that max VCpus on single ESXI host should ideally be 48 vCPUs (same as Logical CPUs)? that would be ratio 2:1?

Many thanks all for your responses

3 Replies
Immortal
Immortal

This is a subject for a protracted discussion and there's no quick one-liner answer. If you want to know more about NUMA and vNUMA, I'd recommend you read the (now free) ebook here as it has all that information and more you'd want to know. As a short answer, always try to follow these guidelines:

  1. Always add sockets over cores to your VMs unless you have a specific licensing-related issue that demands you must also add cores.
  2. Start your VMs off at 1 vCPU and only add what it needs. Make a data-driven decision to add more resources. This is where vROps can help.
Enthusiast
Enthusiast

I've found these two links to have helpful information

Decoupling of Cores per Socket from Virtual NUMA Topology in vSphere 6.5 - frankdenneman.nl

Virtual Machine vCPU and vNUMA Rightsizing - Rules of Thumb - VMware VROOM! Blog - VMware Blogs


There is a slight difference in how vNUMA functions in vSpehre 6.5 compared to 6.0 but the info on these pages helped me understand most sizing considerations.

Commander
Commander

Also if you have money or can claim it back take a look at

VMware vSphere 6.5 Host Resources Deep Dive: Frank Denneman, Niels Hagoort: 9781540873064: Amazon.co...

Explains NUMA and vm configuration and what can impact it among many other usfull things