Arny's incompetence revealed
Robert Morein
Unfortunately, he exposed himself once again, with a complete
misunderstanding of the correct definition of MTBF.
For those of you who like to see Arny with his pants down.
Arny, I am now providing the stream of my personal liquor that was requested
by some. If any of you would like to provide the matches, you are more than
welcome.
Frankly, I am astonished at Arny's ignorance of this subject. Perhaps we
should regard him at his best when he is playing a musical instrument and
singing.
From http://www.storagereview.com/php/tiki/tiki-index.php?page=MTBF
MTBF is the "mean time between failures," that is, the average elapsed time
that passes before a failure occurs in a batch of drives under intense test
conditions.
The initial inclination of those unfamiliar with the spec is to interpret it
as the average expected lifespan of a single drive and either dismiss it as
meaningless (bad) or assume this means their favorite drive will last
decades (bad).
The SCSI-standard MTBF rating of 1.2 million hours, for example, does not
mean that the average unit will run for 137 years before it fails. Likewise,
the other extreme would be 1.2 million drives operating for one hour before
one failed- equally unlikely.
Rather, MTBF is a product of a large quantity of drives (numbering in the
hundreds or low thousands, perhaps) and the number of hours that such a
batch runs before experiencing a failure. If a manufacturer places 1000
units to the test and on average manages to squeeze 50 days of operation out
of the batch between each individual unit failure, that firm's product has
achieved an MTBF of at least 1.2 million hours.
Sometimes, acceleration factors are used for calculating the MTBF of a
drive. These are derived from standard statistical methods. Running the test
at elevated temperatures beyond "normal," for example, will reduce the time
needed to meet a certain number of test hours. Of course, the accuracy of
this acceleration factor has a large effect on the final derived MTBF
number.
That said, there's obviously some room for maneuver left in a "sweet spot"
where firms may attempt to achieve target MTBF by either using more drives
or more hours- there's no set unit count or elapsed time that we may regard
as standard.
MTBF should be regarded as a minimum statement of reliability by the
manufacturer. These days, no manufacturer will spec an enterprise-class
drive below 1.2 million hours. Likewise, no firm will bother with MTBF less
than 400,000 for a desktop-class disk. It is this consistency, rather than
the spec's lack of meaning, that allows one to gloss over these claims.
Last modification date: Saturday 11 of October, 2003 [10:01:12 EDT] by
Eugene
"Arny Krueger" <ar...@hotpop.com> wrote in message
news:irSdnc-yrPY...@comcast.com...
> "Robert Morein" <now...@nowhere.com> wrote in message
> news:gNSdnYD8lef...@comcast.com
>
>
> > A frequently quoted design lifetime is 1,000 hours of burn time.
> > This is not an authoritative figure.
>
> Indeed.
>
>
> Here's a spec sheet for a typical good cheap CD burner
>
> http://www.cdrecordingsoftware.com/liteon5232.html
>
> Relevant spec - MTBF 70,000 (power-on hours). This spec usually presumes
> something like a 10-15% duty cycle. So that would translate to MTBF
7,000 -
> 10,500 hours of actual use.
>
> http://www.tdk.com/cdburners/velocd48xspecs.html
>
> Relevant spec - MTBF 70,000 (power-on hours). This spec says 100,000
hours
> at 25% duty cycle. So that would translate to MTBF 25,000 hours of actual
> use.
>
>
ScottW
Useful life is often defined as the service period during which the
specified MTBF is met (or not exceeded by some amount).
It is much more difficult to demonstrate useful life than MTBF,
therefore you don't see many manufacturers specify it.
Arny's MTBF quotes didn't answer the posters question, How long do
drives last?
ScottW
Robert Morein
"ScottW" <Scot...@hotmail.com> wrote in message
news:bb7403d3.04030...@posting.google.com...
It appears that the design life of a modern laser diode can be as much as
4000 hours. That's the highest I've seen for the wavelength in use. But we
don't know whether the 4000 hour lifetime quoted is in accord with an
accepted MTBF value, or something else.
The owners of Sony Minidiscs were irritated by unexpectedly short lifespans,
so much so that at least one F.A.Q. tries to discriminate between good and
bad revs. It seems the manufacturer has a choice as to how robust a diode he
chooses to use.
It would seem that based upon the specs I've dug up, the useful life (POH
while burning) of a unit COULD be as low as 500 hours, or as high as 4000
hours.
Hours of operation count to laser diode life only when the burner is
actually burning. When idle, or when reading, the laser power consumption is
much lower, and the lifetime much longer.