RE: Storage EMC
- From: "Powell, Mark D" <mark.powell@xxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 9 Jun 2005 13:31:29 -0400
The text below reads to me that 1+0 is more fault tolerant as it is
statistically less likely to fail, which agrees with what I thought and
have repeatedly encountered over the last few years.
IMHO -- Mark D Powell --
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Paul Baumgartel
Sent: Thursday, June 09, 2005 1:14 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Storage EMC
Jared,
I always thought the opposite, that RAID 1+0 is more fault-tolerant,
based on a paper I downloaded. Excerpt:
In either case (0+1 or 1+0), the loss of a single drive does not result
in failure of the RAID system. The difference comes in the chance that
the loss of a second drive from the system will result in the failure of
the whole system. In RAID 0+1, you have to lose one drive from each disk
set to result in the failure of the whole system.
In RAID 1+0, you have to lose all drives in a mirror.
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/(2n-2) 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 [not
included here, sorry], the chance that losing two drives would bring
down the RAID system is 4/7 with a RAID 0+1 system and 1/7 with a RAID
1+0 system.
Paul Baumgartel
On 6/9/05, Jared Still <jkstill@xxxxxxxxx> wrote:
> RAID 0+1 is more fault tolerant than RAID 1+0.
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