From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754560AbYE1T2R (ORCPT ); Wed, 28 May 2008 15:28:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752599AbYE1T2A (ORCPT ); Wed, 28 May 2008 15:28:00 -0400 Received: from lucidpixels.com ([75.144.35.66]:41111 "EHLO lucidpixels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752064AbYE1T17 (ORCPT ); Wed, 28 May 2008 15:27:59 -0400 Date: Wed, 28 May 2008 15:27:58 -0400 (EDT) From: Justin Piszcz To: Chris Snook cc: 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: <483DB0EC.3090403@redhat.com> Message-ID: References: <483D7CE8.4000600@redhat.com> <483DB0EC.3090403@redhat.com> 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 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? But FYI-- In this test, they were regular SATA drives, not special raid-ones (RE2,etc). Thanks for the info! Justin.