Path: utzoo!attcan!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.protocols.nfs
Subject: Re: NFS writes and fsync().
Message-ID: <4194@auspex.auspex.com>
Date: 16 Oct 90 17:14:10 GMT
References: <1990Oct9.152612@objy.objy.com> <thurlow.655748135@convex.convex.com> <1990Oct16.004225.22754@wrl.dec.com>
Organization: Auspex Systems, Santa Clara
Lines: 19

>For example, the reason why NFS clients do write-throughs to the server

By "do write-throughs to the server" do you mean that if a process on an
NFS *client* writes to a file, the data is immediately sent to the
server?

If so, UNIX NFS clients (or, at least, those derived from the Sun code)
do *not* do write-throughs to the server; in fact, they behave like
local-disk UNIX systems, writing dirty blocks out every 30 seconds (or
when the buffer/page is needed), unless somebody on the client has done
an "fcntl()" lock on the file (which causes writes to be done
synchronously on the client, and reads always to go to the server).

To quote NFSD(8):

     biod starts 'nservers' asynchronous block I/O  daemons. This
     command  is  used  on  a  NFS  client to buffer cache handle
     read-ahead and write-behind. The magic number for 'nservers'
     in here is also four.