From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: IO transfer limits Date: Wed, 10 Jan 2007 13:38:08 -0500 Message-ID: <45A53290.1060400@torque.net> References: <8260533.post@talk.nabble.com> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from pentafluge.infradead.org ([213.146.154.40]:43365 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964994AbXAJSiY (ORCPT ); Wed, 10 Jan 2007 13:38:24 -0500 In-Reply-To: <8260533.post@talk.nabble.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: john clyne Cc: linux-scsi@vger.kernel.org john clyne wrote: > Can anyone give me some guidance on where in the IO stack I might be running > into a 512KB limit on IO transfer sizes to an external FC device? I've > checked IO scheduler parameter > (/sys/block//queue/{max_sectors_kb,max_hw_sectors_kb}. Both are set to > 32767. I'm using Qlogic HBAs (qla2312), but I don't see any relevent > parameters. I'm running RHEL 4.0 with a 2.6.9-34 kernel. Any pointers would > be greatly appreciated. John, I discuss the subject in this page: http://www.torque.net/sg/sg_io.html in the section titled: Maximum transfer size per command Mike C. has given you the answer for the block device interface (e.g. via /dev/sda); you should be able to do about 8 times better via the scsi generic interface (e.g. /dev/sg0). Doug Gilbert