RE: Storage array advice anyone?
- From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 15 Dec 2004 08:57:11 -0600
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@xxxxxxxxxxxxx =
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of chris@xxxxxxxxxxxxxxxxxxxxx
Sent: Wednesday, December 15, 2004 6:58 AM
To: cary.millsap@xxxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
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 are all now a bit out of date =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@xxxxxxxxxx>:
> 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@xxxxxxxxxxxxx =3D
> [mailto: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?
>
>
Chris Dunscombe
Christallize Ltd
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