Steve
The apparent low memory utilisation may reflect a large virtual memory. For a file server you want to use the hardware memory and not the disk for cacheing.
Try severely limiting the virtual memory size- virtual memory helps for applications but not for serving files...
Regards
JR
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1