Decide the number of hosts for a cluster depending on the following points:

• Usable space required on the vSAN datastore
• Number of failures to tolerate in the cluster

We have to decide the number of hosts considering a balance between hardware and space:

• A higher number of ESXi hosts and/or disk groups transferred into more hardware costs
• Fewer ESXi hosts and/or disk groups can limit resource availability and compromise performance

For example, if the vSAN cluster is designed with only three ESXi hosts then only a single failure can be protected. We need more than three hosts to protect more than one failure.