how do I tell FreeBSD to sync, for real ?

[user]

On 8 Nov 2005, Lowell Gilbert wrote:

> > So my question is, well first off, why does this happen this way ?  But
> > mostly what I want to know is, is there a more graceful way to tell
> > FreeBSD "sync for real this time, not just for joke only ?"
> > 
> > Basically, is there a nicer way to get what I want than:
> > 
> > sync ; sync ; sync ; sync ; sync ; sync ; sync
> 
> "sleep 30"?
> 
> http://www.usenix.org/publications/library/proceedings/usenix99/full_papers/mckusick/mckusick.pdf



No, I'm not asking "why do I need to sync" ... I understand why I need to
wait, or issue a sync command.  No problems there.

What I am asking is, why is one issuance of `sync` not enough ?  Why is
two not enough ?  Why do I need to issue 6 or 8 of them ?