I was not able to find a documentation for "merge-buffers" feature introduced in D release.

Could you please check it and add feature description if needed? (e.g. into testusage.rst)

In case of "configurable drive options" I think that it is enough to describe configuration options inside 04_vnf.conf as it is now. I don't think that this functionality needs a separate section inside vpserf documentation. May be a note to the generic section of VNF configuration or inside "GOTCHA" section might be useful for user in troubles.