From: Wendy Cheng Subject: Re: [NFS] NFS Digest, Vol 18, Issue 70 (NFS performance problems) Date: Sun, 25 Nov 2007 22:28:43 -0500 Message-ID: <474A3D6B.2060208@redhat.com> References: <47434ED7.4010100@redhat.com> <47435049.1010800@redhat.com> <47445727.5090705@oracle.com> Reply-To: wcheng@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: nfs@lists.sourceforge.net To: chuck.lever@oracle.com Return-path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.91] helo=mail.sourceforge.net) by sc8-sf-list2-new.sourceforge.net with esmtp (Exim 4.43) id 1IwUOW-0002A2-MH for nfs@lists.sourceforge.net; Sun, 25 Nov 2007 19:12:24 -0800 Received: from mx1.redhat.com ([66.187.233.31]) by mail.sourceforge.net with esmtp (Exim 4.44) id 1IwUOc-0002Wp-G9 for nfs@lists.sourceforge.net; Sun, 25 Nov 2007 19:12:30 -0800 In-Reply-To: <47445727.5090705@oracle.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: Chuck Lever wrote: > Hi Wendy- > > That means his old system would have been exposed to data corruption > issues if it crashes (panic, power outage, etc). Using "sync" became > default because async is inherently careless about data integrity. > The data loss is often entirely silent. > > This is explained in the Linux NFS FAQ, question B6. > > See http://nfs.sourceforge.net/index.php#faq_b6 Setting aside NFS for a moment... for a locally mounted filesystem, the file data stays in the cache until write-back occurs. Upon crashing, there are always possibilities that the data could be lost. Journaling filesystems such as EXT3 can only ensure no meta-data corruption, there is no guarantee that data would be saved unless the filesystem is mounted with "sync" option. With non-trivial performance hits, most of the filesystems are hardly mounted with "sync" option. Applications normally understand the problem and whenever required, fsync() and/or similar mechanisms are applied. For Linux NFS servers to deviate from this common practice, by reading the FAQ, I assume something has been done (particularly from client ends) to alleviate the performance hit ? Could you elaborate more about this ? Again, I'm not trying to argue and/or start a flamewar. I have a need to understand more about this issue. The "sync" operation is very expensive for us (cluster filesystem) and I'm under the gun to improve our NFS file serving performance at this moment. -- Wendy ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ NFS maillist - NFS@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nfs _______________________________________________ Please note that nfs@lists.sourceforge.net is being discontinued. Please subscribe to linux-nfs@vger.kernel.org instead. http://vger.kernel.org/vger-lists.html#linux-nfs