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 cluster||Pros||Cons|
|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.