So, a rough calculation gets me
Hours in 3 months = 24*90 = 2160 =approx 2000
If I "run" 500 drives for 3 months and have 1 failure I can claim a
1,000,000 MTBF
2000*500/1 = 1000000
I suppose that's a reasonable test and result, particularly if I weed
out the "infant mortality."
FWIW.
Bruce
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Bruce J. Senn Phone: (518) 388-6664
Senior System Manager FAX: (518) 388-6458
Union College E-mail: [log in to unmask]
Schenectady, NY 12308 WWW: http://www1.union.edu/~sennb
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-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]] On
Behalf Of Bruce Collins
Sent: Wednesday, June 09, 2004 12:22 PM
To: [log in to unmask]
Subject: Re: Disc MTBF restated
In my younger days when I was studying some aspects of risk analysis in
engineering systems, one of the parameters needed to construct fault
trees
would be the MTBF of various components (safety valves, pressure discs,
...). These numbers were very difficult to obtain and tended to be
guesstimates based on past experience or on values for similar
components
from other manufacturers.
Generally, the guesstimate was simply the total system operating time /
number of failures.
So in your case, if you had say 10 drives operating for 6 years and in
that
time you've had 6 failures, an approximation of the MTBF would be 60/6 =
10
years.
You can get some more information including methods to determine various
confidence limits at:
http://www.itl.nist.gov/div898/handbook/apr/section4/apr451.htm
Hope this helps,
Bruce
----- Original Message -----
From: "John Bawden"
> Thanks to all who replied to my original question
> about MTBF on the 4GB model A3647A disc drives. So
> much for manufacturer's published figures. For those
> of you who are still using these drives, can you
> guestimate at the average longevity of these drives
> based on your real world experience? I haven't had any
> failures yet on my production system but I lose one
> every 4-5 months on my older test and development
> system (volume sets to the rescue)and the discs there
> are at least 5-6 years old if not older. I expect I'm
> rapidly approaching the average failure time on
> production and am working on justification for model
> 20 arrays on my Amisys system. Any thoughts pro and
> con? Thanks for any input.
>
> John Bawden
> QualChoice
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