Sites and Subsites
Administrators can create site for each department.
For example;
Site HR, which is meant for Human Resource Department. Only HR staff can view the site and documents inside.
Site Corporate Affairs, which is meant for Corporate Affairs Department. Only Corp Affair staff can view the site and documents inside.
and many other sub sites.
Departmental website can have sub sites. For example, Site IT can have sub sites such as Site Security, Site Infrastructure, and so on.
Each of this departmental website can have separate permissions rights, or shared permissions.
Each of this departmental website has at least one Document Library storage where users can upload documents.