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Date: Tue, 04 Jun 2002 14:51:29 +0200
From: Kasper Dupont <kasperd@daimi.au.dk>
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To: Allan Sandfeld <linux@sneulv.dk>
CC: Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: RAID-6 support in kernel?
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Allan Sandfeld wrote:
> 
> On Monday 03 June 2002 10:57, Kasper Dupont wrote:
> > Roy Sigurd Karlsbakk wrote:
> > > > > RAID-6 layout: http://www.acnc.com/04_01_06.html
> > > >
> > > > If it is supposed to survive two arbitrary disk failures something is
> > > > wrong with that figure. They store 12 logical sectors in 20 physical
> > > > sectors across 4 drives. With two lost disks there are 10 physical
> > > > sectors left from which we want to reconstruct 12 logical sectors.
> > > > That is impossible.
> > >
> > > Might be the diagram is wrong.
> >
> > Could be the case, so until I find another description I will
> > still not know how RAID-6 works.
> >
> It's not just the diagram, the theory is wrong. You need to use at least log2
> n+1 disks for partition if you want to handle any two lost/borked disks. (16
> disks would give 11x diskspace).

But there are other encodings with 2 extra disks that can
handle 2 lost disks. And in general if you need x disks of
space and the ability to recover from y lost disks you can
do the encoding on x+y disks.

Knowing that why do we even consider RAID-6? I guess RAID-6
is a lot faster, is that true?

-- 
Kasper Dupont -- der bruger for meget tid p? usenet.
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