Miguel Medalha wrote:
>>> You might be interested in this article:
>>>
>>> "Why is RAID 1+0 better than RAID 0+1?"
>>> http://aput.net/~jheiss/raid10/
>>>
>>>
>>>
>> The whole raid1+0 or raid0+1 argument was really only relevant in the
>> days of pata when one disk dying on one channel might take out the other
>> disk on the same channel or the controller. Now that we are using SATA,
>> it is MOOT.
>>
>
> No, it is not moot. Have you read the article? It has nothing to do with
> PATA or SATA drives but with probabilities of failure under normal and
> degraded state.
>
> "Mathematically, the difference is that the chance of system failure
> with two drive failures in a RAID 0+1 system with two sets of drives is
> (n/2)/(n - 1) where n is the total number of drives in the system. The
> chance of system failure in a RAID 1+0 system with two drives per mirror
> is 1/(n - 1). So, using the 8 drive systems shown in the diagrams, the
> chance that losing a second drive would bring down the RAID system is
> 4/7 with a RAID 0+1 system and 1/7 with a RAID 1+0 system."
>
Oh sorry, I have never argued about eight drive systems years ago
(didn't have them then, too poor) and there is no argument about raid1+0
being the way to do it beyond four drives. It is too obvious that
stripping three drives and then mirroring them is more risky than making
three mirrors and then stripping them. Any argument then about whether
one should do raid0+1 were really limited to those who had four drive
systems and never thought beyond four drives.
So it is really moot unless one ignores the obvious or fails to think.
> "Another difference between the two RAID configurations is performance
> when the system is in a degraded state, i.e. after it has lost one or
> more drives but has not lost the right combination of drives to
> completely fail."
>
> RAID 1+0 is still more secure."
>
Hear, hear. Man, I should leave the 90s back there.
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