One of the initial decisions you need to make when designing a vSphere Cluster is if you will build a small cluster with larger hosts (scale-up cluster) or a large cluster with smaller hosts (scale-out cluster). There are many factors that work as a catalyst when you choose a scale-up or scale-out cluster. Some of them are as follows:

• Which hardware is ideal for lowering cost, a few larger hosts or a large number of smaller hosts? The answer to this varies in different situations.
• What is the operational cost and complexity over the period of time in maintaining either of these two models?
• What about the other infrastructure components, such as power, cooling, and floor space?
• What is the purpose of this cluster? Is it a desktop virtualization cluster or a server virtualization cluster?

The design decision that you choose depends on the answers to the preceding questions. If you choose to virtualize servers, then this typically requires a large number of hosts with fair capacity. This cluster typically hosts fewer VMs per host. However, the picture is totally different when you virtualize desktops, where you choose fewer hosts with a large capacity to host more VMs per host. You should also consider the maximum capacity of a host in an HA cluster.