RE: Storage array advice anyone?

Cary,

Thanks for that, the paper is very interesting. Your recollection regarding the double-whammy is correct.

The figures used for MTBF, disk size etc. are all now a bit out of date so what I'll do (hopefully before Christmas) is redo the calculations using todays figures and give a few more scenarios (including a comparision with RAID 10, which I believe can be treated as RAID5 with 2 disks in the set, pls correct me if that is an incorrect assumption). Then I'll send the results to the list for info.

Chris

PS Cary would you mind if I send the results to you for review first before sending to the list?

Quoting Cary Millsap <cary.millsap_at_hotsos.com>:

> 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
> * Nullius in verba *
>
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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?
>
>

Chris Dunscombe

Christallize Ltd

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