Describe the issue:
In document Planning your Deployment
In section 7 Infrastructure requirements
In chapter 7.3 Resource requirements

It is really difficult for someone to understand what are the resource requirements per ODF node, especially when ODF is deployed in stretched mode with a minimum number of 4 nodes + arbiter or when ODF is deployed on more than 3 nodes.

Note also that the numbers given in the External row do not correspond to 3 nodes, but correspond only to 1 node, which increases again the confusion.

Describe the task you were trying to accomplish:
I would rephrase the documentation to simplify understanding of the requirements per node.

Suggestions for improvement:

For each ODF node in an Internal deployment mode, the resource requirements can be computed using the following formulas :
CPU (logical) : [ 8 + ( number of drives per node ) * 2 ] cores
RAM (GiB) : [ 19 + ( number of drives per node ) * 5 ] GiB

It is mandatory to have a minimum of 1 drive per node and a minimum of 3 nodes to be able to deploy correctly an ODF Internal mode cluster in a single DC.

For each ODF node in an external deployment mode, the resource requirements are only defined by :
CPU (logical) : 4 cores per node
RAM (GiB) : 16 GiB per node

All related tables 7.1, 7.4, 7.5 can then be easily computed accordingly.

Note that the same computation could be adapted the same way for a deployment on both IBM Power and IBM Z and IBM LinuxONE.

Document URL: Planning Your Deployment

https://access.redhat.com/documentation/en-us/red_hat_openshift_data_foundation/4.13/html/planning_your_deployment/infrastructure-requirements_rhodf#resource-requirements_rhodf

Chapter/Section Number and Title:

In section 7 Infrastructure requirements
In chapter 7.3 Resource requirements

Product Version: ODF 4.x

Environment Details: OCP 4.x