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