RE: Storage array advice anyone?

  • From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 14 Dec 2004 16:38:46 -0600

The probabilities are already worked out, and they're publicly available =
the paper called "RAID: High-Performance, Reliable Secondary Storage" =
ACM Surveys article) by Messrs. Chen, Lee, Gibson, Katz, and Patterson.

Not many people bother to put them into Excel, but when I once played =
the numbers a bit, I realized pretty quickly that the probability of an
outage-causing double-whammy is a lot worse than most people think. The
article mentions that point specifically, if I remember correctly.

The key idea is that the failures of two disks in an array are =
not independent events. Often, the event that just screwed up disk #1 =
has a
higher probability now of screwing up disk #2 before you can fix #1.

Cary Millsap
Hotsos Enterprises, Ltd.
* Nullius in verba *

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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx =
On Behalf Of Jared Still
Sent: Tuesday, December 14, 2004 3:58 PM
To: chris@xxxxxxxxxxxxxxxxxxxxx
Cc: Stephen.Lee@xxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: Storage array advice anyone?

On Tue, 14 Dec 2004 10:47:20 +0000, chris@xxxxxxxxxxxxxxxxxxxxx=20
> My experience is that with either RAID 5 or 10 you have to be =
> unlucky to lose data providing disks are replaced when they fail and =
> for a few days or even more. You are talking extremely remote. It =
might be
> idea to get someone to do the maths and work out the probabilities.

I, for one, have been that unlucky on at least one occasion.=20

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist


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