Re: RAID-6 support in kernel?

Roy Sigurd Karlsbakk (roy@karlsbakk.net)
Mon, 3 Jun 2002 10:28:14 +0200 (CEST)

> > 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. Ok. But I know people like Compaq are
already doing RAID-6.

> OTOH it is possible to construct a system with optimal capacity and
> ability to survive any chosen number of disk failures. This can be
> done using either a Reed-Soloman code or Lagrange interpolation of
> polynomials over a finite field.
>
> However I guess those techniques would be inefficient in software.

Yeah? That's what the hardware RAID vendors all say, and I yet haven't
seen one single test where Linux Software RAID can't beat hardware RAID.
That is also after some testing I did on a high-end intel server at
Compaq's lab in Oslo. How can RAID-6 be so much different?

roy

-- 
Roy Sigurd Karlsbakk, Datavaktmester


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


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