Received: from localhost (maia-3.hub.org [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 6025A9FBAE6 for ; Wed, 30 May 2007 06:42:21 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 20001-06 for ; Wed, 30 May 2007 06:42:14 -0300 (ADT) X-Greylist: delayed 00:06:39.368914 by SQLgrey-1.7.5 Received: from correo2.acens.net (correo2.acens.net [217.116.0.34]) by postgresql.org (Postfix) with ESMTP id 7504C9FB1E0 for ; Wed, 30 May 2007 06:42:17 -0300 (ADT) Received: (qmail 27354 invoked from network); 30 May 2007 09:35:35 -0000 Received: from unknown (HELO sardina) ([83.175.220.10]) (envelope-sender ) by correo2.acens.net (qmail-ldap-1.03) with SMTP for ; 30 May 2007 09:35:34 -0000 From: Albert Cervera Areny Organization: Sedifa, S.L. To: pgsql-performance@postgresql.org Subject: Bad RAID1 read performance Date: Wed, 30 May 2007 11:35:32 +0200 User-Agent: KMail/1.9.5 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200705301135.32236.albert@sedifa.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.051 tagged_above=0 required=5 tests=AWL=0.050, BAYES_50=0.001 X-Spam-Level: X-Archive-Number: 200705/606 X-Sequence-Number: 24996 Hi, after doing the "dd" tests for a server we have at work I obtained: Read: 47.20 Mb/s Write: 39.82 Mb/s Some days ago read performance was around 20Mb/s due to no readahead in md0 so I modified it using hdparm. However, it seems to me that being it a RAID1 read speed could be much better. These are SATA disks with 3Gb of RAM so I did 'time bash -c "dd if=/dev/zero of=bigfile bs=8k count=786432 && sync"'. File system is ext3 (if read many times in the list that XFS is faster), but I don't want to change the file system right now. Modifing the readahead from the current 1024k to 2048k doesn't make any difference. Are there any other tweaks I can make?