Robert Morein
March 8th 04, 04:09 AM
Arny is posturing over in rec.audio.tech.
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" > wrote in message
...
> "Robert Morein" > wrote in message
>
>
>
> > 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.
>
>
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" > wrote in message
...
> "Robert Morein" > wrote in message
>
>
>
> > 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.
>
>