From: Neil Brown Subject: Re: Re: NFS as a Cluster File System. Date: Tue, 14 Jan 2003 06:36:48 +1100 Sender: nfs-admin@lists.sourceforge.net Message-ID: <15907.5456.68906.820989@notabene.cse.unsw.edu.au> References: <3E1DE9D6.7040406@unix.sh> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Lorn Kay , nfs@lists.sourceforge.net, linux-ha@muc.de Return-path: Received: from tone.orchestra.cse.unsw.edu.au ([129.94.242.28] ident=root) by sc8-sf-list1.sourceforge.net with smtp (Exim 3.31-VA-mm2 #1 (Debian)) id 18YAOS-0000yd-00 for ; Mon, 13 Jan 2003 11:37:09 -0800 Received: From notabene.cse.unsw.edu.au ([129.94.242.45] == bartok.orchestra.cse.unsw.EDU.AU) (for ) (for ) (for ) (for ) By tone With Smtp ; Tue, 14 Jan 2003 06:36:52 +1100 To: Alan Robertson In-Reply-To: message from Alan Robertson on Thursday January 9 Errors-To: nfs-admin@lists.sourceforge.net List-Help: List-Post: List-Subscribe: , List-Id: Discussion of NFS under Linux development, interoperability, and testing. List-Unsubscribe: , List-Archive: On Thursday January 9, alanr@unix.sh wrote: > > NFS V3 and before have problems with "cache coherency". That is, the > different nodes in the cluster are not guaranteed to see the same contents. > > I think this is supposed to be fixed in v4. > NFSv4 does not try to "fix" this. It makes no attempts at "cache coherency" beyond what NFSv2/3 provide which is "close to open" cohenrence, meaning that if only one process has a file open at a time, then everythnig will appear coherent, and if multiple processes have the file open at the same time, they need to use record locking. I really don't think total cache coherency is a sensible goal for a network filesystem, even a cluster filesystem. It imposes lots of extra network traffic that most of the time will be of no value. If an application needs some degree of coherence, it should be explicit about it's needs (using open/close or locking) so that the protocol can provide it then, and only then. NeilBrown ------------------------------------------------------- This SF.NET email is sponsored by: FREE SSL Guide from Thawte are you planning your Web Server Security? Click here to get a FREE Thawte SSL guide and find the answers to all your SSL security issues. http://ads.sourceforge.net/cgi-bin/redirect.pl?thaw0026en _______________________________________________ NFS maillist - NFS@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nfs