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From: Roy Sigurd Karlsbakk <roy@karlsbakk.net>
Organization: Pronto TV AS
To: "Christian Vik" <cvik@vanadis.no>
Subject: Re: SV: RAID-6 support in kernel?
Date: Mon, 3 Jun 2002 11:59:33 +0200
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Cc: linux-kernel@vger.kernel.org, Kasper Dupont <kasperd@daimi.au.dk>,
        linux-raid@vger.kernel.org, dstephenson@snapserver.com
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> > > > > 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.

Below is a (patented?) version that works. This is from the linux-raid list

>  A1   A2  (P1) (PA)
> (P2) (PB)  B2   B1
>  C4   C3  (PC) (P3)
> (PD) (P4)  D3   D4
>
> Disclaimer: I took that from Patent 6,353,895.  If you look it up you'll see
> a lot of different schemes and discussion of XOR-based RAID 6, in language
> disguised as English.  You'll also see that I'm listed as the inventor.
> That's four companies back for me, but my current employer unknowingly
> has some rights to it, so I hope it will see the light of day sometime.
>
> Dale Stephenson
> steph@snapserver.com

-- 
Roy Sigurd Karlsbakk, Datavaktmester

Computers are like air conditioners.
They stop working when you open Windows.
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