From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id o9L1x03L161166 for ; Wed, 20 Oct 2010 20:59:00 -0500 Received: from mail.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 2AF5475EC24 for ; Wed, 20 Oct 2010 19:15:15 -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 UcO6Q1rKMhrTpE6G for ; Wed, 20 Oct 2010 19:15:15 -0700 (PDT) Date: Thu, 21 Oct 2010 13:00:09 +1100 From: Dave Chinner Subject: Re: avoid mbox file fragmentation Message-ID: <20101021020009.GG12506@dastard> References: <4CBE2403.8070108@hardwarefreak.com> <20101019234217.GD12506@dastard> <19646.55189.843933.481529@tree.ty.sabi.co.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <19646.55189.843933.481529@tree.ty.sabi.co.uk> 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: Peter Grandi Cc: Linux XFS On Wed, Oct 20, 2010 at 12:50:45PM +0100, Peter Grandi wrote: > However, I am a fan of having *default* physical preallocation, > because as a rule one can trade off space for speed nowadays, and > padding files with "future growth" tails is fairly cheap, and one > could modify the filesystem code or 'fsck' to reclaim unused space > in "future grown" tails. When writing lots of small files (e.g. unpacking a kernel tarball), leaving space at the file tail due to preallocation (that will never get used) means that the file data is now sparse on disk instead of packed into adjacent blocks. The result? Instead of the elevate merging adjacent file data IOs into a large IO, they all get issued individually, and the seek count for IO goes way up. Not truncating away the specualtive prealocation beyond EOF will cause this, too, and that slows down such workloads by an order of magnitude.... So, Peter, you don't get the pony because we gave it to someone else. ;) Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs