From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: SCSI disk speed inconsistency Date: Wed, 05 Oct 2005 08:00:15 +1000 Message-ID: <4342FB6F.4070100@torque.net> References: <4340F4AB.3070107@cdac.in> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from zorg.st.net.au ([203.16.233.9]:7091 "EHLO borg.st.net.au") by vger.kernel.org with ESMTP id S964988AbVJDV71 (ORCPT ); Tue, 4 Oct 2005 17:59:27 -0400 In-Reply-To: <4340F4AB.3070107@cdac.in> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Karthik Sarangan Cc: Linux SCSI Mailing List Karthik Sarangan wrote: > I get a read speed of 69MBps from my SCSI disk and a write speed of > 49MBps from the same. > An IOMeter benchmark on the net says that 68MBps is the sustained speed > for a write. > > Could someone tell me how to increase my IO speed? > > I have a Linux Kernel 2.6 in a RedHat Enterprise Linux WS 4 and I used > the foll. > Read : sg_dd if=/dev/sdb of=/dev/null bs=262144 count=1024 dio=1 > Write: sg_dd if=/dev/zero of=/dev/sdb bs=262144 count=1024 dio=1 Karthik, For accurate timing with "sd" devices use "odir=1" rather than "dio=1". "dio=1" only applies to sg devices so it has no effect in your above example. [Perhaps I should add a warning about this in sg_dd.] Also with sg_dd you should use "bs=512" and read about the "bpt=" option in the man page. Also look at the "blk_sgio=0|1" and the "time=1" option. Doug Gilbert