Received: from localhost (maia-1.hub.org [200.46.204.191]) by postgresql.org (Postfix) with ESMTP id DB6949FBB8F for ; Tue, 27 Feb 2007 13:56:25 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.191]) (amavisd-new, port 10024) with ESMTP id 51199-06 for ; Tue, 27 Feb 2007 13:56:13 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from exchange.g2switchworks.com (mail.g2switchworks.com [63.87.162.25]) by postgresql.org (Postfix) with ESMTP id BEAB19FBB6E for ; Tue, 27 Feb 2007 13:56:12 -0400 (AST) Received: from 10.10.1.37 ([10.10.1.37]) by exchange.g2switchworks.com ([10.10.1.2]) with Microsoft Exchange Server HTTP-DAV ; Tue, 27 Feb 2007 17:56:07 +0000 Received: from state.g2switchworks.com by mail.g2switchworks.com; 27 Feb 2007 11:56:07 -0600 Subject: Re: Opinions on Raid From: Scott Marlowe To: Joe Uhl Cc: pgsql-performance@postgresql.org In-Reply-To: <1172581920.28858.1176750095@webmail.messagingengine.com> References: <1172581920.28858.1176750095@webmail.messagingengine.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Message-Id: <1172598967.20651.72.camel@state.g2switchworks.com> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 (1.4.6-2) Date: Tue, 27 Feb 2007 11:56:07 -0600 X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.019 tagged_above=0 required=5 tests=AWL, BAYES_50, SPF_PASS, UNPARSEABLE_RELAY X-Spam-Level: X-Archive-Number: 200702/325 X-Sequence-Number: 23379 On Tue, 2007-02-27 at 07:12, Joe Uhl wrote: > We have been running Postgres on a 2U server with 2 disks configured in > raid 1 for the os and logs and 4 disks configured in raid 10 for the > data. I have since been told raid 5 would have been a better option > given our usage of Dell equipment and the way they handle raid 10. Some controllers do no layer RAID effectively. Generally speaking, the cheaper the controller, the worse it's gonna perform. Also, some controllers are optimized more for RAID 5 than RAID 1 or 0. Which controller does your Dell have, btw? > I > have just a few general questions about raid with respect to Postgres: > > [1] What is the performance penalty of software raid over hardware raid? > Is it truly significant? We will be working with 100s of GB to 1-2 TB > of data eventually. For a mostly read system, the performance is generally pretty good. Older linux kernels ran layered RAID pretty slowly. I.e. RAID 1+0 was no faster than RAID 1. The best performance software RAID I found in older linux kernels (2.2, 2.4) was plain old RAID-1. RAID-5 was good at reading, but slow at writing.