Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id ECB326322FF for ; Thu, 5 Aug 2010 21:32:03 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.29]) (amavisd-maia, port 10024) with ESMTP id 59259-02 for ; Fri, 6 Aug 2010 00:31:56 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from mail.catalyst.net.nz (bertrand.catalyst.net.nz [202.78.240.40]) by mail.postgresql.org (Postfix) with ESMTP id 7F9346324CF for ; Thu, 5 Aug 2010 21:31:56 -0300 (ADT) Received: from localhost (localhost [127.0.0.1]) by mail.catalyst.net.nz (Postfix) with ESMTP id CD21131C4C for ; Fri, 6 Aug 2010 12:31:51 +1200 (NZST) X-Virus-Scanned: Debian amavisd-new at catalyst.net.nz Received: from mail.catalyst.net.nz ([127.0.0.1]) by localhost (bertrand.catalyst.net.nz [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id j5USunGwmjv8 for ; Fri, 6 Aug 2010 12:31:51 +1200 (NZST) Received: from [IPv6:2404:130:0:1000:222:15ff:fe5c:2471] (unknown [IPv6:2404:130:0:1000:222:15ff:fe5c:2471]) (Authenticated sender: mark.kirkwood) by mail.catalyst.net.nz (Postfix) with ESMTPSA id 008FF31C1E for ; Fri, 6 Aug 2010 12:31:50 +1200 (NZST) Message-ID: <4C5B57F6.8070104@catalyst.net.nz> Date: Fri, 06 Aug 2010 12:31:50 +1200 From: Mark Kirkwood User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.11) Gecko/20100713 Thunderbird/3.0.6 MIME-Version: 1.0 To: pgsql-performance@postgresql.org Subject: Re: Advice configuring ServeRAID 8k for performance References: <4C5B4A0C.5080508@catalyst.net.nz> <201008051658.13399@hal.medialogik.com> In-Reply-To: <201008051658.13399@hal.medialogik.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.79 tagged_above=-10 required=5 tests=BAYES_50=0.8, T_RP_MATCHES_RCVD=-0.01 X-Spam-Level: X-Archive-Number: 201008/84 X-Sequence-Number: 39927 On 06/08/10 11:58, Alan Hodgson wrote: > On Thursday, August 05, 2010, Mark Kirkwood > wrote: > >> Normally I'd agree with the others and recommend RAID10 - but you say >> you have an OLAP workload - if it is *heavily* read biased you may get >> better performance with RAID5 (more effective disks to read from). >> Having said that, your sequential read performance right now is pretty >> low (151 MB/s - should be double this), which may point to an issue >> with this controller. Unfortunately this *may* be important for an OLAP >> workload (seq scans of big tables). >> > Probably a low (default) readahead limitation. ext3 doesn't help but it can > usually get up over 400MB/sec. Doubt it's the controller. > > Yeah - good suggestion, so cranking up readahead (man blockdev) and retesting is recommended. Cheers Mark