Squeezing Virtual Machines Out of CPU Cores

virtual machine per cpu core Are you trying to squeeze every CPU cycle out of your dual, quad or hex core processors for making more VMs per core?

Unfortunately for those who like to over-clock CPUs for gaming, over utilizing CPU doesn’t quite work the same on virtual machine hosts (ESX/ESXi/XenServer or Hyper-V).

How many Virtual Machines Per Core?

From my experience, I know you can get anywhere from 8 – 10 vCPUs per core, but I have found a sweet spot of 4 VMs (that’s right I said VMs not vCPUs) per core will provide decent performance for the user and not affect hardware performance.

Remember, you don’t want users waiting 30 – 60 seconds for a reboot,  logon or screen refresh…

Too many VMs or vCPU per core will cause lag and the same thing goes for over utilizing memory which is another topic of concern. Over utilization of CPU cores and memory will cause system users frustration due to poor VM performance. (Newer versions of ESXi have improved this but it’s still risky to over provision.)

[ad code=2 align=center]

What Eric has to Say about Virtual Machines Per Core

Eric Siebert has written an excellent article on SearchNetworking.com called “Sizing server hardware” which goes into “nuts and bolts” details for sizing virtual host server hardware.

My 1 to 4 ration for VM density per logical CPU is my best practice but Eric goes into much more detail.

Always! Always! Think of the users experience when considering your best practices.

Sure, deploying a 100 VMs on a single host sounds good, but what kind of performance and experience will users have?

I’ve had my share of complaints over slow virtual servers and believe me, you don’t want users to start complaining that your (that’s right, your!) virtual servers are slow.

Rule of Thumb on VMs Per Core

Rule of thumb: Keep it simple, 4 VMs per CPU core – even with today’s powerful servers.

Don’t use more than one vCPU per VM unless the application running on the virtual server requires two or unless the developer demands two and calls your boss. VMs with one vCPU run more efficient and from my experience nobody seems to notice, except for – maybe, over-clockers!

Here’s something I wrote a while back:

“The measurement of a successful virtual infrastructure deployment is not how many VMs can be hosted per host, it’s how many users can be satisfactorily serviced without them knowing they are using virtual technology. Virtualization should be invisible. Once users start noticing foot prints in the snow, it’s over…”

Your turn to share your tips and comments on VMs per CPU core optimization?


  1. William Savage
  2. Abdullah

Leave a Reply

vSphere Data Protection EOA
Finding The Best vSphere Backup Replacement For VDP (3 Alternatives)

Important Notification: vSphere Data Protection (VDP) End of Availability (EOA) That...

vSphere 6
8 Updates That Make vSphere 6 Better – Keith Barker

Editor’s note: Keith Barker has been a CBT Nuggets Trainer since 2012. Some...

VMware Interview Questions
25 VMware Interview Questions And Answers: Tough & Technical (Download PDF)

Free VMware vSphere Interview Guide In this VMinstall Guide, I’ll share...

Project Photon
VMware Project Photon: Technical Review for Linux Admins

My quick and dirty review of Project Photon. I was very happy...

The Best Blockchain Jobs
10 Best Blockchain Jobs Near You (Perfect Match For DevOps Skills)

We’ll cover the best Blockchain jobs in a minute but first, let...

DevOps Plan
Best DevOps Strategy Hack (Winners Start With Why)

What is DevOps? It’s a model. It’s a culture. It’s a...

DevOps Tools Download
DevOps Toolchain: Download 3 Free Tools Used By Pros (Ansible, Git, Jenkins)

Hack Your Resume with DevOps Skills Lately, I’ve been getting a...

DevOps Guide
The Best Microsoft DevOps Skills: 25+ For Windows SysAdmins

What is Microsoft DevOps? This is an interesting question because first off,...

Assessing Your Company's Cloud Readiness
13 Cloud Readiness Assessment Tips To Guide Your Migration Success (Updated)

Planning your migration to the cloud? If you’re planning to move...

How Bare Metal Virtualization Made Cloud Computing A Reality
How Bare Metal Virtualization Made Cloud Computing A Reality

An Overview of Bare Metal Virtualization Let’s start by explaining what...

Advantages of Cloud Computing
Advantages of Cloud Computing (Private versus Public)

Advantages of Cloud Computing Whether you’re an enterprise IT department planning...

Free Offical Amazon VPC & EC2 Cloud Guides for Beginners

Free Cloud Guides for Beginners Are you researching Amazon’s AWS Virtual...

What’s So Interesting About Woz U?

On 10/12/2017, I had the privilege of attending the AZ Tech...

tensorflow training
TensorFlow Tools for Beginners (7 Easy Takeaways To Get You Started)

Introduction To Deep Learning As a follow-up to my book review...

job rut
How To Get MOVING When You’re Stuck In A Career Rut (Video)

You worked hard to get your degree and after graduation you...

Storage Engineer Skills
Why Storage Engineer Skills Are HOT! (Can You Say Big Data?)

3 BIG Skills New Storage Engineers Are Missing Out On… Behind...

VULTR Reviews
VULTR Review And Comparison: Best VPS Platforms Now Thru 2018
Website for Small Business
Best Small Business Website Packages (6 Alternatives That Rank!)
Click here to learn how to Optimize WordPress Speed
WordPress Speed Optimization: Learn To Rank Higher In Google
Best Hosting for WordPress
Case Study: Best VPS For Easy WordPress Migration