From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: Why is NCQ enabled by default by libata? (2.6.20) Date: Sat, 31 Mar 2007 08:55:45 -0400 Message-ID: <460E5A51.7010601@emc.com> References: <4608B2B9.7090503@garzik.org> <460964BA.8090101@garzik.org> <711F1620-F483-4CC2-83D6-F2DD577AB5BB@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mexforward.lss.emc.com ([128.222.32.20]:36954 "EHLO mexforward.lss.emc.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751545AbXCaM4F (ORCPT ); Sat, 31 Mar 2007 08:56:05 -0400 In-Reply-To: <711F1620-F483-4CC2-83D6-F2DD577AB5BB@gmail.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Mark Rustad Cc: Jeff Garzik , Justin Piszcz , linux-kernel@vger.kernel.org, IDE/ATA development list Mark Rustad wrote: > On Mar 27, 2007, at 1:38 PM, Jeff Garzik wrote: > >> Mark Rustad wrote: >>> reorder any queued operations. Of course if you really care about >>> your data, you don't really want to turn write cache on. >> >> That's a gross exaggeration. FLUSH CACHE and FUA both ensure data >> integrity as well. >> >> Turning write cache off has always been a performance-killing action >> on ATA. > > Perhaps. Folks I work with would disagree with that, but I am not > enough of a storage expert to judge. My statement mirrors the > judgement of folks I work with that know more than I do. You can easily demonstrate that disabling write cache on a S-ATA or ATA drive will drop your large file write performance by 50% - just try writing 10MB files to disk. ric