Re: RAID 1 or 5 ?

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#435

From: Malcolm Weir
Date: Thu, 29 Jul 1999 00:00

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On Thu, 29 Jul 1999 12:01:25 +0200, Ren� K�hnen Wiesemes
<koehnen.pad@sni.de> caused to appear as if it was written:

>none of your suggested solutions will work
>for 2 simultaneously HD failures:

True.

>RAID 1 (stripping) gives none fault tolerance at all.
>If you mirrored two RAID 1 groups, only one part
>can be out of order without data loss.

You're confusing RAID0, which is striping, with RAID1, which is mirroring.

With the suggested scheme, drive 0 would be mirrored with drive 2, drive 1
with drive 3, then stripe the two pairs together.  You can lose the *right*
two drives (e.g. 0 and 1 or 3, 1 and 0 or 2, etc). but not the wrong pair
(i.e. 0 and 2, 1 and 3)

>> If I am interested in having storage fault tolerant up to
>> 2 x HD failure, which option will be good ?
>>
>> Option #1 RAID 1 with 4 HDs, i.e. 2 pairs
>> Option #2 RAID 5 with 4 HDs, i.e. 3 in group, 1 standby

Malc.

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From: malc@cwix.com (Malcolm Weir)
Subject: Re: RAID 1 or 5 ?
Date: 1999/07/29
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