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Date: Tue, 16 Apr 2002 09:19:01 -0700 (PDT)
From: Scott Hess <scott@avantgo.com>
To: Chris Dillon <cdillon@wolves.k12.mo.us>
Cc: David Drum <david@mu.org>,
	FreeBSD DB List <freebsd-database@FreeBSD.ORG>
Subject: Re: Raid configuration
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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
> 
> 
> 
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