From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: SATA RAID5 speed drop of 100 MB/s Date: Sun, 24 Jun 2007 19:52:54 +0400 Message-ID: <467E9356.1030200@msgid.tls.msk.ru> References: <20070620224847.GA5488@alinoe.com> <4679B2DE.9090903@garzik.org> <20070622214859.GC6970@alinoe.com> <467CC5C5.6040201@garzik.org> <20070623125316.GB26672@alinoe.com> <467DA1F5.2060306@garzik.org> <467E5C5E.6000706@msgid.tls.msk.ru> <20070624125957.GA28067@gallifrey> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from hobbit.corpit.ru ([81.13.94.6]:21797 "EHLO hobbit.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755695AbXFXPw6 (ORCPT ); Sun, 24 Jun 2007 11:52:58 -0400 In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Justin Piszcz Cc: "Dr. David Alan Gilbert" , Jeff Garzik , Carlo Wood , Tejun Heo , Manoj Kasichainula , linux-kernel@vger.kernel.org, IDE/ATA development list Justin Piszcz wrote: > Don't forget about max_sectors_kb either (for all drives in the SW RAID5 > array) > > max_sectors_kb = 8 > $ dd if=/dev/zero of=file.out6 bs=1M count=10240 > 10737418240 bytes (11 GB) copied, 55.4848 seconds, 194 MB/s > > max_sectors_kb = 128 > 10737418240 bytes (11 GB) copied, 22.6298 seconds, 474 MB/s Well. You're comparing something different. Yes, this thread is about linux software raid5 in the first place, but I were commenting about [NT]CQ within a single drive. Overall, yes, the larger your reads/writes to the drive becomes, the faster its linear performance is. Yet you have to consider real workload instead of very synthetic dd test. It may be good approcsimation of a streaming video workload (when you feed a large video file over network or something like that), but even with this, you probably want to feed several files at once (different files to different clients), so single-threaded test here isn't very useful. IMHO anyway, and good for a personal computer test. /mjt