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Date: Mon, 3 Jun 2002 10:24:17 +0200 (CEST)
From: Roy Sigurd Karlsbakk <roy@karlsbakk.net>
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To: Derek Vadala <derek@cynicism.com>
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        Tedd Hansen <tedd@konge.net>, Christian Vik <christian@konge.net>,
        Lars Christian Nygaard <lars@snart.com>
Subject: Re: RAID-6 support in kernel?
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> You can always fake this effect by combining two 8-disk RAID-5s into a
> RAID-0. It's not technically RAID-6, but can withstand a 2-disk failure,
> although not _any_ 2-disk failure. However, it's my understanding that
> RAID-6 cannot withstand _any_ two disk failure either (see the above
> thread). 

It'll waste 9 drives, giving me a total capacity of 7n instead of 14n. 
And, by definition, RAID-6 _can_ withstand _any_ two-drive failure.

> I also suspect that the use of dual RAID-5s combined with the CPU overhead
> of ATA will kill most systems under any kind of load. For that matter, the
> 2x parity hit from RAID-6 probably wouldn't make you CPU too happy either,
> even if there was a kernel driver that implemented it.

With a 1500MHz Athlon on a typical file server where there's not much 
writes, the CPU is sitting there chrunching RC5-64 som 99,95 % of the 
time. I don't think it'll make much differnce with today's CPUs

roy

-- 
Roy Sigurd Karlsbakk, Datavaktmester

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

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