X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id 3941A9DC861 for ; Tue, 31 Jan 2006 21:26:18 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 10287-03 for ; Tue, 31 Jan 2006 21:26:21 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from cassarossa.samfundet.no (cassarossa.samfundet.no [129.241.93.19]) by postgresql.org (Postfix) with ESMTP id 830F19DC827 for ; Tue, 31 Jan 2006 21:26:15 -0400 (AST) Received: from trofast.sesse.net ([129.241.93.32]) by cassarossa.samfundet.no with esmtp (Exim 4.50) id 1F46lA-0000KW-51; Wed, 01 Feb 2006 02:26:12 +0100 Received: from sesse by trofast.sesse.net with local (Exim 3.36 #1 (Debian)) id 1F46lD-0008R0-00; Wed, 01 Feb 2006 02:26:15 +0100 Date: Wed, 1 Feb 2006 02:26:15 +0100 From: "Steinar H. Gunderson" To: Luke Lonergan Cc: "Jeffrey W. Baker" , pgsql-performance@postgresql.org Subject: Re: Huge Data sets, simple queries Message-ID: <20060201012615.GA31927@uio.no> Mail-Followup-To: Luke Lonergan , "Jeffrey W. Baker" , pgsql-performance@postgresql.org References: <1138737838.5648.4.camel@toonses.gghcwest.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Operating-System: Linux 2.6.14.3 on a x86_64 X-Message-Flag: Outlook? --> http://www.mozilla.org/products/thunderbird/ User-Agent: Mutt/1.5.11 X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.071 required=5 tests=[AWL=0.071] X-Spam-Score: 0.071 X-Spam-Level: X-Archive-Number: 200601/503 X-Sequence-Number: 16981 On Tue, Jan 31, 2006 at 12:47:10PM -0800, Luke Lonergan wrote: >> Linux does balanced reads on software >> mirrors. I'm not sure why you think this can't improve bandwidth. It >> does improve streaming bandwidth as long as the platter STR is more than >> the bus STR. > ... Prove it. FWIW, this is on Ultra160 disks (Seagate 10000rpm) on a dual Opteron running Linux 2.6.14.3: cassarossa:~# grep md1 /proc/mdstat md1 : active raid1 sdf6[1] sda6[0] cassarossa:~# dd if=/dev/sda6 of=/dev/null bs=8k count=400000 [system at about 35% wait for I/O and 15% system, according to top] 400000+0 records in 400000+0 records out 3276800000 bytes transferred in 54,488154 seconds (60137842 bytes/sec) [system at about 45% wait for I/O and 7% system -- whoa?] 400000+0 records in 400000+0 records out 3276800000 bytes transferred in 52,523771 seconds (62386990 bytes/sec) I'm not sure if it _refutes_ the assertion that the Linux RAID-1 driver can do balancing of sequential reads, but it certainly doesn't present very much evidence in that direction. BTW, sda and sdf are on different channels of a dual-channel (onboard, connected via PCI-X) Adaptec board, so I doubt the bus is the limiting factor. /* Steinar */ -- Homepage: http://www.sesse.net/