vSphere clusters Scale Up or Scale Out?

By | January 17, 2016

In my previous post, I justified why to create the vSphere Management Cluster. In this short post we discuss vSphere Clusters: Scale Up and Scale Out. What's difference?

Scale Up - vSphere cluster based on larger ESXi hosts (adding more processors and RAM)

Scale Out - vSphere cluster based on smaller ESXi hosts (servers with less processors and RAM)

Type of clusterProsCons
Scale up- Costs! (licensing, power consumption)
- Better utilization Transparent Page Sharing (TPS)
- Ability to support larger VMs
- Less chance for CPU contention and better memory performance (larger NUMA node size)
- Host failure causes, a larger number of VMs are impacted because they needed to be restarted
- Higher HA overhead
- Potential for Network or I/O problems due to larger number of VMs per host
- Less hosts = less flexibility for DRS to load balance VMs between them
Scale out- Host failure does not cause, a larger number of VMs are impacted
- Less HA overhead
- More hosts = greater flexibility for DRS to load balance VMs between them
- Easy upgrade ESXi hosts (firmware, vSphere etc) - less VMs to evacuate
- Costs (additional servers, licensing, power consumption, more network ports required)
- Less utilization of TPS
- Possible CPU contention (less cores)

So which one to use? It depends on for example: configuration of VMs, type of servers (blade or rack) or security standards (e.g. DMZ servers).

I prefer Scale Out Clusters based on Blade Servers. Easy upgrade, "be green" 🙂 and  a smaller number of VMs are impacted and have to be restarted when a host fails.

Author: Mariusz

Architect (~ 15 years experience based on passion...) with strong background as a System Administrator and Engineer. Focused on Data Center Solutions: Virtualization/Cloud Computing and Storage/Backup Systems. Currently living in Poland.

One thought on “vSphere clusters Scale Up or Scale Out?

  1. Basavaraj Navalgund

    Hi Mariusz,

    Nice insite into scale Up and scale Out and these are very points to kept in before infra changes.

    Raj Navalgund


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