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From: mlinar@poisson.usc.edu (Mitch Mlinar)
Newsgroups: comp.misc
Subject: Re: disk drive life expectancies
Message-ID: <4464@oberon.USC.EDU>
Date: Fri, 18-Sep-87 18:23:34 EDT
Article-I.D.: oberon.4464
Posted: Fri Sep 18 18:23:34 1987
Date-Received: Sun, 20-Sep-87 13:27:05 EDT
References: <1118@gilsys.UUCP> <303@kksys.UUCP>
Sender: nobody@oberon.USC.EDU
Reply-To: mlinar@poisson.usc.edu (Mitch Mlinar)
Distribution: na
Organization: University of Southern California, Los Angeles, CA
Lines: 61
Keywords: MTBF, power cycling, lifespan

>In article <1118@gilsys.UUCP> mc68020@gilsys.UUCP (Thomas J Keller) writes:
><....Take the Seagate ST-225 piece of trash, for example.  A very popular
><drive, largely due to its low price, this drive has a 4000 hour MTBF....
>
>Actually, from the info I have it appears the ST-225 has a very
>respectable 20,000 hour mtbf....  I am including a copy of part of an earlier
>posting which may help to clarify this:
>
><>>   Unfortunately, many of the  winchesters  used  in  the  PC  and
><>>   small-UNIX  machines  only  have a MTBF rate of ~3000 hours.  A
>
><>While I too have seen a few small winchesters die at around 3000 hours,
><>most are rated for 5 years life span.  If you look at the OEM hardware
><>manual for seagate drives, of which I own one, the entire series is
><>rated at a MTBF (failure time) of approx 25,000 hours.  That is more than
><
><I recently received a brochure from Seagate which gives specs on their
><current drive lines... It shows the ST125, 138, 213, 225 and 251 as
><having a MTBF of 20,000 hours, and the ST4026, 4038, 4051 and 4096 as
><having a MTBF of 15,000 hours.  At 20,000 hours, this would be about 2
><years and four months... at 15,000 hours it works out to a bit under
><one year and nine months, assuming 24 hour a day operation.
><
><They -do- list the drives as having a service life of five years, and
><a mean time to repair (MTTR) of thirty minutes.

Well, to add to all this, you must understand HOW these numbers are determined,
which is usually by test of a small group under CONTROLLED conditions.  As
you have heard me write before, I have tested 100's of drives for both lifetime
and controller card driver debugging.  This put me in close contact (still
am) with several dealers who collectively push out 100+ hard drives a month
for micros.  The following position is based on this experience.

I have YET to see a hard drive last 3 years in an IBM PC or any other micro,
limited cooling and all.  (I am talking about 3 years of USE, not "I use my
machine once or twice a week/month and it has lasted 25 years....")
This can range from as low as one year to as high as 2.5 years (excluding
infant mortality).  Drives include CDC, Tandon, CMI, Shugart, Maxtor, Seagate,
Rodime, MicroSci, and a bunch that you may not have heard of.  (If someone
wants the FULL boring list of manufacturers, let me know.)  Yes, SOME are
better than others, in the MICROCOMPUTER environment.  Dealers reported 
Tandons and Seagates being returned as fast as they could order replacements
whereas Rodime and Maxtor were rarely returned.  (Not to slight the others,
but these are the ones I remember.)  Bearing seizures were the most common
followed by media failures.  Plated media virtually eliminates media failures,
but at a premium in price.

In short, for the current consumer market drives, assume about 2 years of
moderate use before failure.  If you use your drive once or twice a week,
you are better off to shut it down rather than spin it.  My rule of thumb
is that use within 24 hours determines whether to shutdown or leave spinning.
It is interesting to note that nearly all failures for home computers are
bearing seizures; these drives spend only a fraction of their life accessing
media and the rest just merrily spinning away.

Finally, MTTR, by many manufacturers, has come to mean Mean Time to
Replace.  Yes, it only takes 30 minutes or less to replace the hard drive.
However, if you don't have current backups or $$$ for a new one, this is
meaningless.

-Mitch