From owner-freebsd-performance@FreeBSD.ORG  Sat Feb 14 07:08:57 2009
Return-Path: <owner-freebsd-performance@FreeBSD.ORG>
Delivered-To: freebsd-performance@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id F352C1065675
	for <freebsd-performance@freebsd.org>;
	Sat, 14 Feb 2009 07:08:56 +0000 (UTC)
	(envelope-from freebsd@sopwith.solgatos.com)
Received: from sopwith.solgatos.com
	(pool-173-50-231-101.ptldor.fios.verizon.net [173.50.231.101])
	by mx1.freebsd.org (Postfix) with ESMTP id 791378FC1E
	for <freebsd-performance@freebsd.org>;
	Sat, 14 Feb 2009 07:08:56 +0000 (UTC)
	(envelope-from freebsd@sopwith.solgatos.com)
Received: by sopwith.solgatos.com (Postfix, from userid 66)
	id 1A6B5B64F; Fri, 20 Feb 2009 22:49:36 -0800 (PST)
Received: from localhost by sopwith.solgatos.com (8.8.8/6.24)
	id GAA14352; Sat, 21 Feb 2009 06:16:08 GMT
Message-Id: <200902210616.GAA14352@sopwith.solgatos.com>
To: freebsd-performance@freebsd.org
In-reply-to: Your message of "Thu, 12 Feb 2009 11:57:02 GMT."
	<49940E8E.1080107@thekeelecentre.com> 
Date: Fri, 20 Feb 2009 22:16:08 +0000
From: Dieter <freebsd@sopwith.solgatos.com>
Subject: Re: Extremely slow write speeds to disk : FreeBSD 7.1 and Dell SAS
	6/iR Adapter 
X-BeenThere: freebsd-performance@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Performance/tuning <freebsd-performance.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-performance>,
	<mailto:freebsd-performance-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-performance>
List-Post: <mailto:freebsd-performance@freebsd.org>
List-Help: <mailto:freebsd-performance-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-performance>,
	<mailto:freebsd-performance-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 14 Feb 2009 07:08:57 -0000

> > But the issue is that writing to disk is extremely slow...i.e. 14Mb per
> > second....
> > 
> > If I install any other linux distribution, like CentOS, write speek is
> > the way it should be..it averages around 190Mb+ per second
> > 
> > I was hoping if it were at all possible for you to assist me in with a
> > later RAID Controller Driver for the SAS 6/iR Adapter
> 
> Try:
> hw.mpt.enable_sata_wc=1
> in /boot/loader.conf and reboot.
> 
> Assuming you are using SATA drives, the write cache is disabled by 
> default. This reenables it. The mpt manpage holds more information.

Just keep in mind that turning the disk's write cache on puts your
data at risk.  :-(

The correct solution is NCQ.