From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757291AbYE2VJV (ORCPT ); Thu, 29 May 2008 17:09:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752889AbYE2VJE (ORCPT ); Thu, 29 May 2008 17:09:04 -0400 Received: from lucidpixels.com ([75.144.35.66]:50835 "EHLO lucidpixels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751591AbYE2VJC (ORCPT ); Thu, 29 May 2008 17:09:02 -0400 Date: Thu, 29 May 2008 17:08:59 -0400 (EDT) From: Justin Piszcz To: Kasper Sandberg cc: Chris Snook , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, xfs@oss.sgi.com Subject: Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++) In-Reply-To: <1212055050.25169.33.camel@localhost> Message-ID: References: <483D7CE8.4000600@redhat.com> <483DB0EC.3090403@redhat.com> <1212055050.25169.33.camel@localhost> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 29 May 2008, Kasper Sandberg wrote: > On Wed, 2008-05-28 at 15:27 -0400, Justin Piszcz wrote: >> >> On Wed, 28 May 2008, Chris Snook wrote: >> >>> Justin Piszcz wrote: >>>> >>>> >>>> On Wed, 28 May 2008, Chris Snook wrote: >>>> >>>>> Justin Piszcz wrote: >>>>>> Hardware: >>>>>> >>>>> Given that one of the greatest benefits of NCQ/TCQ is with parity RAID, >>>>> I'd be fascinated to see how enabling NCQ changes your results. Of >>>>> course, you'd want to use a single SATA controller with a known good NCQ >>>>> implementation, and hard drives known to not do stupid things like disable >>>>> readahead when NCQ is enabled. >>>> Only/usually on multi-threaded jobs/tasks, yes? >>> >>> Generally, yes, but there's caching and readahead at various layers in >>> software that can expose the benefit on certain single-threaded workloads as >>> well. >>> >>>> Also, I turn off NCQ on all of my hosts that has it enabled by default >>>> because >>>> there are many bugs that occur when NCQ is on, they are working on it in >>>> the >>>> libata layer but IMO it is not safe at all for running SATA disks w/NCQ as >>>> with it on I have seen drives drop out of the array (with it off, no >>>> problems). >>>> >>> >>> Are you using SATA drives with RAID-optimized firmware? Most SATA >>> manufacturers have variants of their drives for a few dollars more that have >>> firmware that provides bounded latency for error recovery operations, for >>> precisely this reason. >> I see--however, as I understood it there were bugs utilizing NCQ in libata? > You wouldnt happen to have some more information about this? i havent > personally had problems yet, but i havent used it for very long - but > since it comes activated by DEFAULT, i would assume it to be relatively > stable? Not off-hand, check LKML and my email address from early this year or last year and/or the ide-list. Justin.