Proper Mix for the job
Quote: "their parallel access is still a world-beater, but one wonders for how long"
For a very very very long time if the metadata is on flash at least for NFS
Up to 90% of NFS v3 IOPs on a production system deal with metadata. v4 somewhat improves on that, but not by much.
SMB/CIFS is a more interesting case as it allows a lot of client side caching of metadata. However even in that case flash can (and will) do miracles with metadata read performance.