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Recover lost files on CD or DVD

When your CD is dying...

The observation

Traduction en Français La récupération de fichiers sur CD ou DVD

Updated information (Jan-06):

Now, Kurt Gerecke, an expert from IBM Germany, speaks up and tells the awful truth on ComputerWorld: Burned CD and DVD: limited life span around 2-5 years.

But he also considers that hard disc drives are no better and advises you to use magnetic tapes.

CD-ROM are annonced as being able to live a century-long life. CD-R are supposed to be nearly as sturdy. However, it seems that experience is not fully supporting these claims.

While, in my collection of 600 albums, I have many audio CD which were bought in the 80's and that spent part of their time in the gloves compartment of a -sometimes- overheated small car, none ever failed me. 20 years already and no random failure. I'd guess a century is a reasonable target.

On the other hand, my experience with CD-R tells me that they should not be used for storage. And I mean "any kind of storage".

In the last four years I burnt around 500 silver discs for various archival purposes. I have been using several CD writers from different brands (Toshiba, Teac, etc.) and various interface technologies (IDE, SCSI, etc.) The empty discs where coming from all kinds of brands. So, I'd say I have a fairly good statistical idea of this kind of market and it is depressing: CD-R media is not worth it.

Around 20% of all discs are unreadable just a few months (maybe a year) after writing.

It would be re-assuring - in a sense - if I could say that some brands are better than others. Actually, I can't. No-name dirt-cheap blank media is just what you should expect: Nothing survives after a year.

The origin

Even if it is difficult to know for sure, I have been trying to identify the most plausible source of this fast decay. The technical literature usually points to two dangers.

The first one is heat. High temperatures tends to deteriorate the sensitive surface. So, you are advised to keep your discs in a temperate room environment (for really long term, some corporations go to the extremes of near freezing lows in controlled humidity).

The other enemy of your data is light. This, I could easily confirm with some discs I forgot on the corner of an old stack of paper. Direct light will transform the sensitive surface to the point that the shadow of objects is visible. Bad, bad, bad! So avoid light at all costs. It may be as easy as storing discs in closed cupboards instead of an open shelf (this was my own mistake). Don't be fooled by the plastic cases: They reduce the amount of light (and UV light) received by the CD, but they are not enough.

Software solutions?

When things went so wrong that you are starting to get errors from the discs you read, what should you do? I am unsure. There are many products on the market that claim that they can read the data from your failing media. Possible candidates are:

Unfortunately my experience seems to prove that when the disc is still without errors, these products are (obviously) useless; Later, I never suceeded in recovering lost data. It seems that the best ones repetitively read the same sector applying statistic laws to discard errors and find the right data. Unfortunately, this is not very different from what all modern CD drives do silently when they discover a first error. So, you are not informed early of the failures of the media. When you hear about them (when an error is reported), it means that the siuation is already out of control. It means that tools like CDcheck should be used preventively. If reading a disc is still feasible but request some retries, it is time to restart from a fresh copy and dump the old failing disc . If you are willing to maintain this kind of long term commitment...

The real solution (my solution)

My preference goes to something else. I decided that the combination of rapidly failing optical media and ugly prophylactic procedures was too much for me.

Currently, I am commited to purely magnetic storage: Hard disc drives are not much more expensive than CD-R and they have an excellent longevity (this is even better if you allow the disc to sleep when unused for long periods of time): More than 100,000 hours between failures is not uncommon and this is more than 11 years of permanent use.

Even better

Despite this sturdiness, hard discs are not eternal. A power spike can be fatal, electronic components are prone to rare but random failures, plain bad luck is a fact of life.

In my eyes, RAID technology is the way to go. Already, a number of recent motherboards include either RAID-0 or RAID-5 technology that allow to use several disc at the same time to improve reliability at the cost of some lost storage space. I'll provide more about this in later writings.

 


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Latest update: 30-oct-08

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