From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Martin W. Schlining III" Subject: Large Sequential Reads Being Broken Up. Why? Date: Mon, 30 Jan 2006 10:20:16 -0500 Message-ID: <43DE2EB0.2040700@datadirectnet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from postoffice.datadirectnet.com ([64.213.193.141]:44430 "EHLO postoffice.datadirectnet.com") by vger.kernel.org with ESMTP id S932313AbWA3PTJ (ORCPT ); Mon, 30 Jan 2006 10:19:09 -0500 Received: from localhost (localhost [127.0.0.1]) by postoffice.datadirectnet.com (Postfix) with ESMTP id 1A65236B2D3C for ; Mon, 30 Jan 2006 07:19:09 -0800 (PST) Received: from postoffice.datadirectnet.com ([127.0.0.1]) by localhost (postoffice.datadirectnet.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 22782-10 for ; Mon, 30 Jan 2006 07:19:08 -0800 (PST) Received: from [127.0.0.1] (ddneng.com [70.88.130.31]) by postoffice.datadirectnet.com (Postfix) with ESMTP id 3B694340275F for ; Mon, 30 Jan 2006 07:19:08 -0800 (PST) Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org I am running a program on my Linux box which is asking for 2M IO (reads and writes) with the file handle being opened with the O_DIRECT flag. However, the IO being put out on the wire is no larger than 512K. My target device is the SCSI block device (/dev/sdb in this case). What is preventing me from getting large IO through the SCSI block layer? How can I fix it? The sg device can achieve the 2M IO size, so I know its at least possible. How can I improve the IO size for the SCSI block layer? Details: Dell 2850 server with dual Xeons, 1G RAM OS: Linux racerx 2.6.11.4-21.10-smp #1 SMP Tue Nov 29 14:32:49 UTC 2005 x86_64 x86_64 x86_64 GNU/Linux Emulex LP11000 Fibre Channel HBA using driver version 8.0.13 (changing the driver hasn't helped, so far) I set the lookahead value pretty large to improve read performance (hdparm -a) The scheduler for this device is anticipatory. Any ideas? Thanks, Martin Schlining