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Date: Thu, 06 Jun 2002 10:28:28 +0200
From: Kasper Dupont <kasperd@daimi.au.dk>
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To: Derek Vadala <derek@cynicism.com>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-raid@vger.kernel.org
Subject: Re: RAID-6 support in kernel?
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Derek Vadala wrote:
> 
>   RAID-1 --------> RAID-5 (D0,D1,D2,D3,P0)
>               |--> RAID-5 (D0,D1,D2,D3,P0)
>    (four disks used for data, only one from each RAID-5 can fail)

Wrong, any three disks can fail. If the one RAID has only
one faulty disk, the other RAID can have any number of
faulty disks without loosing data.

> 
> With RAID-10:
> 
>   RAID-0 --------> RAID-1 (D0,D0)
>               |--> RAID-1 (D1,D1)
>               |--> RAID-1 (D2,D2)
>               |--> RAID-1 (D3,D3)
>               |--> RAID-1 (D4,D4)
>    (five disks used for data, one from each mirror can fail)
> 
> With RAID-50:
> 
>   RAID-0 --------> RAID-5 (D0,D2,D4,D6,P0)
>               |--> RAID-5 (D1,D3,D5,D7,P0)
> 
>    (two disks wasted only one from each RAID-5 can fail)
> 
> I believe that I/O performance would be similar for each
> configuration. I'll try to run some tests in the next few days.

I'd guess that depends on the access patterns.

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