From owner-freebsd-hackers@FreeBSD.ORG  Sun May 31 23:55:59 2009
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 7E749106566B
	for <freebsd-hackers@freebsd.org>; Sun, 31 May 2009 23:55:59 +0000 (UTC)
	(envelope-from wojtek@wojtek.tensor.gdynia.pl)
Received: from wojtek.tensor.gdynia.pl (wojtek.tensor.gdynia.pl
	[IPv6:2001:4070:101:2::1])
	by mx1.freebsd.org (Postfix) with ESMTP id 6E2FE8FC2D
	for <freebsd-hackers@freebsd.org>; Sun, 31 May 2009 23:55:58 +0000 (UTC)
	(envelope-from wojtek@wojtek.tensor.gdynia.pl)
Received: from wojtek.tensor.gdynia.pl (localhost [IPv6:::1])
	by wojtek.tensor.gdynia.pl (8.14.3/8.14.3) with ESMTP id n4VNtrf3027124;
	Mon, 1 Jun 2009 01:55:54 +0200 (CEST)
	(envelope-from wojtek@wojtek.tensor.gdynia.pl)
Received: from localhost (wojtek@localhost)
	by wojtek.tensor.gdynia.pl (8.14.3/8.14.3/Submit) with ESMTP id
	n4VNtrsC027121; Mon, 1 Jun 2009 01:55:53 +0200 (CEST)
	(envelope-from wojtek@wojtek.tensor.gdynia.pl)
Date: Mon, 1 Jun 2009 01:55:53 +0200 (CEST)
From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: krad <kraduk@googlemail.com>
In-Reply-To: <0229B3BF1BE94C82AA11FD06CBE0BDEF@uk.tiscali.intl>
Message-ID: <alpine.BSF.2.00.0906010153570.27108@wojtek.tensor.gdynia.pl>
References: <20090530175239.GA25604@logik.internal.network>
	<20090530144354.2255f722@bhuda.mired.org>
	<20090530191840.GA68514@logik.internal.network>
	<20090530162744.5d77e9d1@bhuda.mired.org>
	<A5BB2D2B836A4438B1B7BD8420FCC6A3@uk.tiscali.intl>
	<20090531201445.GA82420@logik.internal.network>
	<alpine.BSF.2.00.0905312355240.26545@wojtek.tensor.gdynia.pl>
	<0229B3BF1BE94C82AA11FD06CBE0BDEF@uk.tiscali.intl>
User-Agent: Alpine 2.00 (BSF 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: freebsd-hackers@freebsd.org, xorquewasp@googlemail.com
Subject: RE: Request for opinions - gvinum or ccd?
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 31 May 2009 23:55:59 -0000

> should really use raidz2 in zfs (or some double parity raid on other
> systems) if you are worried about data integrity. The reason being the odds
> of the crc checking not detecting an error are much more likely these days.
> The extra layer of parity pushes these odds into being much bigger

you are right with capacity but not performance. once again - RAIDz is 
more like RAID-3 not RAID-5, RAIDz2 is somehow like RAID3 with double 
parity disk.

you will get IOps from RAIDz/RAIDz2 set not much more than from single 
drive, even on reads.

But if it's used for mostly linear reading big files you are right.