Quick and Dirty vSphere Cluster Sizer

This is just a quick calculator tool I whipped up for sizing up a vSphere cluster, assuming your requirements are based on core counts and RAM. At least, this is one of the more frequently used sizing methods I’ve seen for new application / project deployments, so hopefully this will make life easier if you have to do such calculations.


Cluster Requirements

  • Required Number of Cores: You probably already have a table of app VMs and their core count requirements, so this will be a total of the number of cores required within the cluster
  • Required RAM (GB): Same as the above, but for RAM
  • Utilization Ceiling (%) Before Redundancy: What is the maximum utilization allowed for the base cluster, without considering redundancy. Allows for possible growth, burst, and overhead. Preferably remain below 80%.
  • Total Number of Cores: Total number of CPU cores after taking into account the Utilization Ceiling. Calculated using Required Number of Cores / Utilization Ceiling * 100
  • Total RAM (GB): Total amount of RAM after taking into account the Utilization Ceiling. Calculated using Required RAM / Utilization Ceiling * 100
  • Redundant Systems (n+x): Additional number of hosts to add into a cluster for redundancy for HA during failover scenarios. This is the number of host outages the cluster can sustain, before cluster capacity drops below either the Total Number of Cores or Total RAM specified above.

Host Configuration

  • Number of Sockets: Number of sockets within a single physical host
  • Cores / CPU or Socket: Number of cores within each processor
  • RAM (GB): Amount of RAM to be configured

Within the example, I’ve configured it for an average Sandy Bridge 2 Socket server with balanced memory at 192GB (2x 4 memory channels of each CPU => 24GB spread evenly to each memory channel)

Cluster Specification

  • Minimum number of hosts required: Minimum number of hosts required, defined by number of cores or RAM required, whichever is higher.
  • Hosts required for redundancy: Number of hosts required after the addition of redundant hosts for failover scenarios.

You can download the Quick and Dirty vSphere Cluster Sizer here. This program is provided as-is, without any guarantees/warranties, so do use it responsibly and be sure that you counter-check its results. It’s a tool for convenience, so feedback is always welcome on how to enhance the features!

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