Don't buy Western Digital

Josh Coates jcoates at archive.org
Thu Feb 3 07:20:59 MST 2005


>They started publishing never-seen-before
>mean-time-before-failure (MTBF) statistics (e.g. 100,000 hours) which
>would indicate they expect their product to operate without fail for a
>decade.

actually, the published MTTF/MTBF stats are typically around
500,000-1,000,000 hours (but most vendors don't publish these anymore) and
they should not be taken literally - for many reasons.

drives failure rates follow a 'bathtub' curve - most live a long time, but
some die really young, and some die really old (this curve makes a bathtub
shape when measuring probability of failure over time.)  the warranty is
intended to cover infant mortality, so having a year warranty should be just
fine.

heat and duty-cycle are the two major factors in determining the actual
longevity of a drive.

when manufacturers come up with their MTTF numbers, they test them at 25C
(whats typically used for IC testing) and pick either 'fully-on' duty-cycle
or 'barely-on' duty-cycle, depending on the product.

when they come up with their theoretical MTTF, it translates to an annual
failure rate in the .5%-2% range - but the actual failure rate of drives can
be twice as high because no one really keeps their drive at 25C and the
actual duty-cycle is usually not 'always-on' or 'never-on' - it's somewhere
inbetween.

for example, if a vendor says they have a MTTF of 500,000 hours at 25C and
10% duty-cycle (eg. vendor sells it for "near-line storage"), this implies a
1.75% annual failure rate (factoring out infant mortality and old age)

in reality, you will probably run the disk closer to 40C and at say 20%
duty-cycle, which will end up making the annual failure rate just over 4%.
your probability of failure over an operational period of 3 years will be
about 11.6% and if you operate it over 10 years, it will be just over 33%.
of course, this is only for one disk - and it doesn't factor in the
'old-age' portion of the bathtub curve.  if you have several disks, the
probability of you having a disk failure will increase substantially.

moral of the story is: no, your disk probably won't last 10 years.

sorry - i sort of went off there, but i'm kind of a disk geek.

Josh Coates
http://www.jcoates.org

-----Original Message-----
From: plug-bounces at plug.org [mailto:plug-bounces at plug.org]On Behalf Of
Doran Barton
Sent: Wednesday, February 02, 2005 10:06 PM
To: Provo Linux Users Group Mailing List
Subject: Re: Don't buy Western Digital


Not long ago, James Lance proclaimed...
> I'm mostly venting here, but don't waste your money on western digital
drives.
> I bought a 120 gig last december and it failed on me this month.  Usually
that
> is no big deal, I've had drives fail in shorter amounts of time.
>
> The problem is wd has a terrible warranty.  It is only one year long.  I
know
> the community (slashdot...) has raised a stink about this, but it just bit
> me.  So I'm out a drive, and WD lost my business.
>
> On the bright side WD will be happy to sell me a new drive at a marginally
> reduced price...  Looks like a good business plan if you are willing to
buy
> their drives again.

About four years ago, all the major hard drive manufacturers did an
interesting thing: They started publishing never-seen-before
mean-time-before-failure (MTBF) statistics (e.g. 100,000 hours) which
would indicate they expect their product to operate without fail for a
decade. Publishing those kinds of statistics, you'd think they'd pack a
warranty to go along with their confidence, but the standard warranty
silently changed from 3 years to 1 year at the same time.

There are still some drive models from various manufacturers that have 3
year warranties. Some have 5 year warranties.

My advice: Never buy a hard drive with less than a 3 year warranty. Never
buy a hard drive with less than 8 MB of buffer. Never buy a hard drive with
less than 7200 RPM rotational speed (unless it's HUGE, in which case 5400
RPM is alright).

--
fozz at iodynamics.com is Doran L. Barton, president, Iodynamics LLC
Iodynamics: Linux solutions - Web development - Business connectivity
 "Let's enjoy your life. Sometimes you can do it only with lovely color."
    -- Japanese stationary packaging




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