From owner-freebsd-database  Tue Apr 16  9:40: 0 2002
Delivered-To: freebsd-database@freebsd.org
Received: from kali.avantgo.com (shadow.avantgo.com [64.157.226.66])
	by hub.freebsd.org (Postfix) with ESMTP id 787FC37B405
	for <freebsd-database@FreeBSD.ORG>; Tue, 16 Apr 2002 09:39:56 -0700 (PDT)
Received: from river.avantgo.com ([10.11.30.114]) by kali.avantgo.com with Microsoft SMTPSVC(5.0.2195.3779);
	 Tue, 16 Apr 2002 09:39:55 -0700
Date: Tue, 16 Apr 2002 09:40:19 -0700 (PDT)
From: Scott Hess <scott@avantgo.com>
To: FreeBSD DB List <freebsd-database@FreeBSD.ORG>
Subject: Re: Raid configuration
In-Reply-To: <Pine.LNX.4.44.0204160908060.5530-100000@river.avantgo.com>
Message-ID: <Pine.LNX.4.44.0204160935420.6159-100000@river.avantgo.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-OriginalArrivalTime: 16 Apr 2002 16:39:55.0377 (UTC) FILETIME=[56CC4610:01C1E565]
Sender: owner-freebsd-database@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-database.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-database>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-database>
X-Loop: FreeBSD.ORG

So, why'd I draw the diagram if I wasn't going to refer to the disks by
name at any point?  If 2 disks fail, there are six possible pairs.  
RAID10 stays up if (A|B)&(C|D) stay up (4/6).  RAID01 can only stay up if
(A&C)|(B&D) stay up (2/6).

Sigh,
scott

On Tue, 16 Apr 2002, Scott Hess wrote:
> Additionally, consider two setups:
> 
> RAID10 (stripe of mirror)
> +---------+
> |+-------+|
> || A = B ||
> |+-------+|
> |+-------+|      
> || C = D ||
> |+-------+| 
> +---------+
> 
> RAID01 (mirror of stripes)
> +-----------+
> |+---+ +---+|
> || A | | B ||
> ||   |=|   ||
> || C | | D ||
> |+---+ +---+|
> +-----------+
> 
> Both have the same uptime for single-disk failures.  For two-disk
> failures, RAID10 stays up for 2/3 of the cases, while RAID01 only stays up
> in 1/3 of the cases.
> 
> Later,
> scott
> 
> 
> On Sun, 14 Apr 2002, Chris Dillon wrote:
> > On Sun, 14 Apr 2002, David Drum wrote:
> > 
> > > > And when you only have a four-drive configuration, it makes no
> > > > difference which one you use since the chances of a total failure
> > > > is exactly the same either way.  Any more drives than that and you
> > > > definately want RAID10.  :-)
> > >
> > > The chances of total failure may be the same, but the effort
> > > required to rebuild the RAID is not.  If you have 4 9GB disks in a
> > > RAID 0+1 and one goes bad, you have to mirror 18GB once the drive is
> > > replaced.  If you have a RAID 1+0, you only have one drive to
> > > mirror, and not a stripe.
> > 
> > Ah, yes, I hadn't thought of what it would take to rebuild one.  In
> > that case, RAID 0+1 looks like the loser in all situations.
> > 
> > --
> >  Chris Dillon - cdillon@wolves.k12.mo.us - cdillon@inter-linc.net
> >  FreeBSD: The fastest and most stable server OS on the planet
> >  - Available for IA32 (Intel x86) and Alpha architectures
> >  - IA64, PowerPC, UltraSPARC, and ARM architectures under development
> >  - http://www.freebsd.org
> > 
> > 
> > 
> > To Unsubscribe: send mail to majordomo@FreeBSD.org
> > with "unsubscribe freebsd-database" in the body of the message
> > 
> 
> 
> 


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-database" in the body of the message