From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id o8T0ULSG008374 for ; Tue, 28 Sep 2010 19:30:22 -0500 Received: from mail.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 8745FAFFA8 for ; Tue, 28 Sep 2010 17:31:18 -0700 (PDT) Received: from mail.internode.on.net (bld-mail15.adl6.internode.on.net [150.101.137.100]) by cuda.sgi.com with ESMTP id rnFsloMDGKQyTR2R for ; Tue, 28 Sep 2010 17:31:18 -0700 (PDT) Date: Wed, 29 Sep 2010 10:31:10 +1000 From: Dave Chinner Subject: Re: allocsize mount option Message-ID: <20100929003110.GH5665@dastard> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Ivan.Novick@emc.com Cc: Timothy.Heath@emc.com, xfs@oss.sgi.com On Tue, Sep 28, 2010 at 02:53:46PM -0400, Ivan.Novick@emc.com wrote: > Hi all, > > According to the documentation the allocsize mount option: "Sets the > buffered I/O end-of-file preallocation size when doing delayed allocation > writeout" > > Will this value limit "extent" sizes to be be no smaller than the allocsize? No - it's specualtive preallocation. > I have set the following mount options: > (rw,noatime,nodiratime,logbufs=8,allocsize=512m) /me wishes he could run a sed script across the internet. noatime implies nodiratime, and logbufs=8 is the default, so you only need "noatime,allocsize=512m" > And yet, depending on the workload, the extent sizes are often 1 or 2 orders > of magnitude lower than 512 MB ... It's speculative and there's no guarantee that it can find a big enough extent to complete the full allocsize allocation. Also, when you close the file the speculative allocation beyond EOF is truncated away. This is a particular problem with NFS servers. > If I wanted to do further reading on the subject, can someone point me to an > approximate location in the code where the size of a newly created extent is > determined? Start here: fs/xfs/xfs_iomap.c::xfs_iomap_write_delay() Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs