SCSI CD burner

[CRC]

On Mon, 18 Sep 2006 13:58:47 -0500, John Foust <jfoust at threedee.com>  
wrote:

> At 02:35 PM 9/16/2006, CRC wrote:
>> The basic problem with commercial CD burners/players is that they
>> keep the laser diodes on when powered, although at the low power
>> required for reading. The life of run-of-the-mill laser diodes is on
>> the order of 10,000 (10.000) hours. Consequently, if you keep your
>> system on all the time you can expect one to two years of useful life
>> from the beast (some longer, some shorter).  From <http:// 
>> www.wtec.org/ loyola/opto/ad_rohm.htm>:
>
> That document dates from 1994.  You'd think that manufacturers would
> want to increase MTBF and eliminate failures as quickly as possible,
> so I find it hard to believe that LEDs are left on inside today's
> CD/DVDs just because it's hard to turn them off and they don't want
> to improve lifetimes.  This info may be entirely relevant for
> 1980s drives, who knows?

My intent was to address classic computer equipment. MTBFs of Laser  
Diodes (LDs - not LEDs) has definitely increased over the last 10  
years. However, access to information of the ones used in current CD  
equipment is privy only to large scale manufacturers. Looking at LDs  
that are used in fiber optic transmission shows a substantial  
increase in MTBF over the past 10 years. However, I would hold off on  
buying into the BlueRay recorders - blue LDs are still have low MTBFs.

CD equipment production has progressed to commodity class and every  
penny represents a margin change of $10k / 1M units - design is done  
by taking out things until the unit doesn't work :=)). Adding the  
circuitry to turn off the laser is not difficult, but it costs money...

> What sorts of other ancedotes and
> claimed facts do we have?
>
>  From the CD-R FAQ: http://www.cdrfaq.org/faq05.html
>
> Subject: [5-2] How long do CD recorders last? (1998/04/06)
>
>   The MTBF (Mean Time Between Failures) on these drives is  
> typically 50,000
>   to 100,000 hours, and they come with a 1 year warranty. Compare  
> that to
>   hard drives rated at between 500,000 and 1,000,000 hours with a 3  
> or 5
>   year warranty and that should give you some idea. Most of the drives
>   available today weren't meant for mass production of CD-Rs. The only
>   exceptions are the venerable Philips CDD 522, Kodak PCD 600, and  
> Sony CDW-900E.
>

I assume that the FAQ uses manufacturers stated MTBF - there is no  
citation for their source.

> By 2004, MTBF for consumer CD/DVD were up to 60K to 100K hours:
>
> http://www.computingondemand.com/reviews/storage-LiteOn-LDW-411S/ 
> page1.shtml
>
> And perhaps their MTBF was calculated with a 2% duty cycle, which
> would still mean they expect a consumer DVD-R to be able to burn
> several thousand discs.  I suspect consumer losses are due more to
> dust and crud on discs...  unless of course you simply don't want to
> trust manufacturer-provided MTBFs.

In most cases, the criteria for the MTBF is not stated as indicated  
by your suposition. One has to look at MTBF at temperature since  
Optek shows a factor of greater than 25 in MTBF between 25 and 70 C.  
If the tests were run at 20C and you run the device at 50C you can  
expect 6K and 9K hours vs 70K and 100K hours respectively (based on  
ratios from the Optek MTBF data for their OPV200 series high  
reliability LDs). At 70C it's around 1.5K and 2K hours.  It's not  
that I don't trust the manufacturer, it's just that there is  
insufficient info and the manufacturer's shills will present their  
most favorable data.

Besides the mechanical/electrical failures, which there are many, the  
LDs power loss generally results in the inability to record and read  
reliably. Note that the LD does not touch the disk and unless it is  
used in a smoky/cruddy atmosphere there should be no failure in the  
optical link. In trying to repair a good number of CDR/W I have  
recovered only several units by cleaning the LD lens. Recording  
generally uses virgin disks and an occasional brushing of the lens  
does help.
>
> Your average $50 Wal-Mart DVD drive has a 70K MTBF:
>
> http://www.liteon.com/prod/getProduct.do? 
> cid=1_7_13&xml_id=4_2&menu_id=4_2_7

Note that the stated MTBF is in POH - power on hours - not usage  
hours. I guess if you use it all bets are off :=P

	CRC