🚀 go-pugleaf

In article 
<EF4B31908F2A7BAC.E7C81737A020640C.DF7A420979E4C82E@lp.airnews.net>, 
malc@cwix.com says...
>
>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
>


true
RAID 5 would only support the loss of one drive at a time
and i can't think of anything that would support the loss of "any" 
2 drives at once

* a warm global spare can be set to start backing up immediately OR
  to wait until the production shift is over & then rebuild
  (sometimes "degraded" state is all you can handle)

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