From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: SATA RAID5 speed drop of 100 MB/s Date: Sat, 23 Jun 2007 18:43:01 -0400 Message-ID: <467DA1F5.2060306@garzik.org> References: <20070620224847.GA5488@alinoe.com> <4679B2DE.9090903@garzik.org> <20070622214859.GC6970@alinoe.com> <467CC5C5.6040201@garzik.org> <20070623125316.GB26672@alinoe.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:40881 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751245AbXFWWnJ (ORCPT ); Sat, 23 Jun 2007 18:43:09 -0400 In-Reply-To: <20070623125316.GB26672@alinoe.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Carlo Wood , Jeff Garzik , Tejun Heo , Manoj Kasichainula , linux-kernel@vger.kernel.org, IDE/ATA development list Carlo Wood wrote: > Is it possible that the measurement with "hdparm -tT" returns a higher > value for some setting, but that the over-all real-life performance > drops? IN THEORY, RAID performance should /increase/ due to additional queued commands available to be sent to the drive. NCQ == command queueing == sending multiple commands to the drive, rather than one-at-a-time like normal. But hdparm isn't the best test for that theory, since it does not simulate the transactions like real-world MD device usage does. We have seen buggy NCQ firmwares where performance decreases, so it is possible that NCQ just isn't good on your drives. Jeff