From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: Why is NCQ enabled by default by libata? (2.6.20) Date: Wed, 28 Mar 2007 10:48:51 -0400 Message-ID: <460A8053.3040209@garzik.org> References: <20070327161616.31448.qmail@science.horizon.com> <460A7EE7.5070101@cfl.rr.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]:45301 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752237AbXC1Ot1 (ORCPT ); Wed, 28 Mar 2007 10:49:27 -0400 In-Reply-To: <460A7EE7.5070101@cfl.rr.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Phillip Susi Cc: Justin Piszcz , linux@horizon.com, htejun@gmail.com, linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org Phillip Susi wrote: > Justin Piszcz wrote: >> I would try with write-caching enabled. >> Also, the RAID5/RAID10 you mention seems like each volume is on part of >> the platter, a strange setup you got there :) > > Shouldn't NCQ only help write performance if write caching is > _disabled_? Since write cache essentially is just non tagged command > queuing? NCQ provides for a more asynchronous flow. It helps greatly with reads (of which most are, by nature, synchronous at the app level) from multiple threads or apps. It helps with writes, even with write cache on, by allowing multiple commands to be submitted and/or retired at the same time. Jeff