Received: from localhost (maia-4.hub.org [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 312779FB350 for ; Wed, 28 Feb 2007 23:28:52 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-new, port 10024) with ESMTP id 02011-01 for ; Wed, 28 Feb 2007 23:28:48 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from wolff.to (wolff.to [66.93.197.194]) by postgresql.org (Postfix) with SMTP id 685309FB34E for ; Wed, 28 Feb 2007 23:28:48 -0400 (AST) Received: (qmail 15693 invoked by uid 500); 1 Mar 2007 03:28:46 -0000 Date: Wed, 28 Feb 2007 21:28:46 -0600 From: Bruno Wolff III To: Peter Kovacs Cc: Tom Lane , Carlos Moreno , pgsql-performance@postgresql.org Subject: Re: Two hard drives --- what to do with them? Message-ID: <20070301032846.GA14102@wolff.to> Mail-Followup-To: Bruno Wolff III , Peter Kovacs , Tom Lane , Carlos Moreno , pgsql-performance@postgresql.org References: <45DF3B15.1070609@3times25.net> <200702231330.57014.josh@agliodbs.com> <45DF5DA9.90002@commandprompt.com> <45DF6154.5090205@3times25.net> <1d4e0c10702231425ke37a732y36e241902fe0aa55@mail.gmail.com> <45DF94BF.6050904@3times25.net> <45E0A500.1010707@commandprompt.com> <45E104DD.3080600@mochima.com> <2055.1172375931@sss.pgh.pa.us> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200702/349 X-Sequence-Number: 23403 On Sun, Feb 25, 2007 at 23:11:01 +0100, Peter Kovacs wrote: > A related question: > Is it sufficient to disable write cache only on the disk where pg_xlog > is located? Or should write cache be disabled on both disks? With recent linux kernels you may also have the option to use write barriers instead of disabling caching. You need to make sure all of your stacked block devices will handle it and most versions of software raid (other than 1) won't. This won't be a lot faster, since at sync points the OS needs to order a cache flush, but it does give the disks a chance to reorder some commands in between flushes.