Datacenters vs Clusters within the vCenter Inventory

Recently I got involved in a discussion about “Creating multiple Datacenters with one Clusters rather than one Datacenter with multiple Clusters”

First of all lets get the definitions of these objects summarized (as stated in the vSphere Datacenter Administration Guide)

Clusters

A collection of ESX/ESXi hosts and associated virtual machines intended to work together as a unit. When you add a host to a cluster, the host’s resources become part of the cluster’s resources. The cluster manages the resources of all hosts. VMware Features like EVC, DRS, DPM and HA are enabled on a per Cluster basis.

Datacenters

Unlike a folder, which is used to organize a specific object type, a datacenter is an aggregation of all the different types of objects needed to do work in virtual infrastructure:

• Virtual machines (and templates)
• Hosts (and clusters)
• Networks
• Datastores

The datacenter defines the namespace for networks and datastores. The names for these objects must be unique within a datacenter. For example, you cannot have two datastores with the same name within a single datacenter, but you can have two datastores with the same name in two different datacenters.

Virtual machines, templates, and clusters need not be unique within the datacenter, but must be unique within their folder.

Objects with the same name in two different datacenters are not necessarily the same object. Because of this, moving objects between datacenters can create unpredictable results. For example, a network named networkA in datacenterA might not be the same network as a network named networkA in datacenterB. Moving a virtual machine connected to networkA from datacenterA to datacenterB results in the virtual machine changing the network it is connected to.

Back to the the discussion about creating multiple Datacenters, this was mainly started because the organization wanted a static “Folder” hierarchy per environment. Since the Datacenter object is the boundary for Folders their environment looked like this:

This design argument can easily be set aside since it’s possible to create Subfolders as well. So it could also look like this:

while preserving the one Datacenter design which, from a logic perspective they had.

The key message here is to be sure that you have thought well about the design decisions and that you preserve logics as much as possible to keep a clear view even when the the environment grows.