RE: Storage array advice anyone?

Chris,

I agree that the MTTF numbers these days are a lot different than when = the
article was originally published. But I think that the structure of the calculations has remained pretty constant.

I think you're right about how to model RAID level 0+1 (1+0)-it's just a degenerate case of RAID level 5, where G=3D2.

I hate to become the bottleneck on getting your work in front of = everyone.
There are lots of people on this list who can do the job as well or = better
than I can. :) I'll look at it too (time permitting at the time when you send it), but I'd recommend for you to show it on the list as soon as = you're
done.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

Upcoming events:

- Performance Diagnosis 101: 1/4 Calgary
- SQL Optimization 101: 2/7 Dallas
- Hotsos Symposium 2005: March 6-10 Dallas
- Visit www.hotsos.com for schedule details...

-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of chris_at_thedunscombes.f2s.com Sent: Wednesday, December 15, 2004 6:58 AM To: cary.millsap_at_hotsos.com
Cc: oracle-l_at_freelists.org
Subject: 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 are all now a bit out of date = so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 =3D
> in
> the paper called "RAID: High-Performance, Reliable Secondary Storage" =
=3D
> (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 =
=3D
> 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 =3D
> frequently
> not independent events. Often, the event that just screwed up disk #1 =
=3D
> 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 *
>
> Upcoming events:
> - Performance Diagnosis 101: 1/4 Calgary
> - SQL Optimization 101: 2/7 Dallas
> - Hotsos Symposium 2005: March 6-10 Dallas
> - Visit www.hotsos.com for schedule details...
>
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org =3D
> [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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