From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sun, 24 Jun 2007 22:50:30 -0700 (PDT) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with SMTP id l5P5oCds020911 for ; Sun, 24 Jun 2007 22:50:23 -0700 Date: Fri, 22 Jun 2007 09:59:32 +1000 From: David Chinner Subject: Re: Poor performance -- poor config? Message-ID: <20070621235932.GZ85884050@sgi.com> References: <4679951E.8050601@bnl.gov> <46799939.2080503@bnl.gov> <55EF1E5D5804A542A6CA37E446DDC206F5C5AA@mapibe17.exchange.xchg> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55EF1E5D5804A542A6CA37E446DDC206F5C5AA@mapibe17.exchange.xchg> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Sebastian Brings Cc: Justin Piszcz , Robert Petkus , xfs@oss.sgi.com On Thu, Jun 21, 2007 at 08:37:36AM +0200, Sebastian Brings wrote: > Not sure if it makes much sense to set stripe unit and width for a Raid > which appears as a single device. Certainly it does. That way you get stripe aligned allocation and therfore you are much more likely to get full-stripe width writes instead of unaligned writes that force RMW cycles on the RAID controller for parity calculations. > As you state, the "width" of your DS lun is 4 x 512K == 2MB. In case you > don't have write cache enabled each of your 1MB writes will cause the DS > to write to two out of four disks only, causing heavy overhead to create > parity. You're assuming stripe aligned I/O there. That 1MB could hit 3 of the 4 data disks - if you don't have a stripe unit set then that will be the common case. i.e. its worse than you think :/ Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group