Whether it’s Hyper-V® or VMware® or any other virtual environment, growth is inevitable for virtual machines (VM) and workload in any data center setup. IT teams always want to know how many VMs can be created on a physical host, and how much more VM workload can my host resources support? Especially for Hyper-V environment, Microsoft® has augmented and expanded the limits of VM capacity with Hyper-V 2012.


According to this post on Perti, these are the capacity and scalability limits of Hyper-V VMs in windows Server 2012 – which is a drastic improvement on Windows Server 2008 & 2008 R2.

  • Virtual processors per VM: 64
  • Logical processors in hardware: 320
  • Physical memory per host: 4 TB
  • Memory per VM: 1 TB
  • Nodes in a cluster: 64
  • VMs in a cluster: 8000
  • Active VMs: 1,024

So, what happens when all these limits are reached? You just need to add more VMs. And that’s not an easy job for the IT admin. You have to figure out the budget, host resource procurement, and carry out the actual VM creation and assignment. But this is NOT the smart and cost-effective way to scale your VM environment.


Capacity planning is the process of monitoring VM and host resource utilization, while being able to predict when the VMs will run out of resources and how much more workload can be added to them. The benefit is that you will be able to optimize your Hyper-V environment, chart usage trends, reallocate some unused resources to critical VMs, identify and control VM sprawl, and right-size the entire VM environment, without just making a case for resource procurement.


The proactive capacity planning approach would be to identify capacity bottlenecks so that you’re in a position to make an informed decision about VM expansion.


Top Reasons for Capacity Bottlenecks

  • Uncontrolled VM sprawl
  • Enabling HA without accounting for failover
  • Increase in VM reservation
  • Resource pool config changes
  • Natural resource utilization growth
  • Workload changes


Capacity Management: “What If” Analysis

The next step is to perform “What If” analysis to determine how much more load existing VMs will sustain with, and how many more VMs can be created for a specified workload. Third-party virtualization management tools, such as SolarWinds Virtualization Manager provide dedicated capacity management functionality that allows you to perform VM capacity estimations and understand possible expansion.

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Key Questions to be Answered While Performing Capacity Planning

  • How can I detect capacity bottlenecks?
  • How can I predict capacity bottlenecks before they happen?
  • How may VMs can I fit within my current footprint?
  • What if I add more resources (VMs, hosts, storage, network, etc.) to my environment?
  • Which cluster is the best place for my new VM?
  • When will I run out of capacity?
  • How much resource is my average SQL Server®, Exchange, etc. VM using?
  • How much more resources do I need to buy and when?
  • How can I right-size my VMs to optimize existing capacity?


The below capacity planning dashboard in Virtualization Manager tracks and trends CPU, storage IOPS, memory, network throughput and disk space and provides you details into how many more large, medium and small VMs you can add to your Hyper-V and other clusters.


Benefits of Capacity Planning

  • Monitor Hyper-V capacity operations and resource utilization, and forecast resource depletion
  • Optimize IT resources with business requirements and make informed purchase decisions on host resource procurement, VM creation, and overall budget planning
  • Gain insight into VM placement between or within Hyper-V clusters to deploy VMs across clusters efficiently
  • Pinpoint zombie or rogue virtual machines and over or under-allocated VMs to right-size your Hyper-V environment
  • Determine when and where Hyper-V bottlenecks will occur and identify the solutions


Read this TechNet post to learn more about Microsoft Windows Server 2012 Hyper-V Scalability limits.


Watch this short video to learn more about capacity planning and management - explained by Eric Siebert (vExpert)