RE: Storage array advice anyone?

The probabilities are already worked out, and they're publicly available = in
the paper called "RAID: High-Performance, Reliable Secondary Storage" = (an
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 = with
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 = frequently
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.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Jared Still
Sent: Tuesday, December 14, 2004 3:58 PM To: chris_at_thedunscombes.f2s.com
Cc: Stephen.Lee_at_dtag.com; oracle-l_at_freelists.org Subject: Re: Storage array advice anyone?

On Tue, 14 Dec 2004 10:47:20 +0000, chris_at_thedunscombes.f2s.com=20
> My experience is that with either RAID 5 or 10 you have to be =
unbelievably
> unlucky to lose data providing disks are replaced when they fail and =
not
left
> for a few days or even more. You are talking extremely remote. It =
might be
an
> 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

--=20
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

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