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A Starter's guide on recovering damaged and rotten CDs

93 points by nixass 2y ago

xnzakg 2y ago
https://archive.is/djjCY https://archive.is/djjCY Wasn't able to easily decline cookies.
stavros 2y ago
> Dvdisaster can be used to generate error correction code files for an optical disc, which is in good condition. We should then store this ECC file in a safe place. Can't store some data reliably for a long time? You can mitigate it by storing some other data reliably for a long time.
- buran77 2y ago
  If you already have a lot of data on older, less reliable storage formats you have the choice of keeping a full copy all that data on something with higher reliability, or store just a small fraction of it in the form of the ECC file. The first option may be technically more sound but comes with a larger investment in terms of time and money. Second option may be less reliable but with significant savings. It's up to the owner of the data to decide how to balance these.
  - stavros 2y ago
    What sort of higher-reliability options (than a Blu-ray) does a consumer have? I struggle to think of something that's not fairly niche, eg a magnetic tape drive.
    - buran77 2y ago
      > higher-reliability options You'd be comparing to an old optical disc. So almost anything is higher reliability than that, starting with a newer optical disc and probably ending at any cloud storage. > does a consumer have This isn't limited just to your average consumer. DVDs are still in use in libraries and different archives which can't afford to store a full backup. We've had parity checks appended to the very same data to be protected for so long because it does protect from some common failure modes even if not from all. Dvdisaster goes one step beyond and gives the option to store the ECC file elsewhere. Definitely better than nothing and probably even with a very good cost/benefit ratio.
      - self_awareness 2y ago
        buran77 wrote: > You'd be comparing to an old optical disc. So almost anything is higher > reliability than that, starting with a newer optical disc and probably ending > at any cloud storage. Is "cloud" really being considered as a viable backup solution? I mean, some of my CDs are older than most of today's "cloud" servers and can be read just fine.
        buran77 2y ago
        > some of my CDs are older than most of today's "cloud" servers and can be read just fine. And if you're happy being able to recover "some" of your data that's a perfectly legitimate option. Write CDs and DVDs, save to HDDs and SSDs, to the cloud, print on paper, or a combination of all. Only you know your data and its importance. But what you'll want to ask yourself though is how many CDs written since than can't be read just fine. I have books from before electricity was a thing and still am thoroughly convinced paper is not the best for long term preservation. My oldest cloud stored data that I can verify is a 25 year old email in my Yahoo mailbox. I have stamped CDs that survived that long, no written CD that I can think of.
        self_awareness 2y ago
        Well, Yahoo is one of the few e-mail providers that survived the last 25 years. I had e-mails on multiple providers which don't exist since a long time. That brings another question, how do you even know that the cloud company will even exist in the next 25 years? I think Yahoo is now enforcing OAuth authorization. Maybe next step is to remove IMAP? How do you know that they're not planning it? The point is that it's impossible to try and predict how the cloud will look like in the future. One day we can end up receiving an e-mail that we need to download all data from the cloud because they're ending their operation. And the future of paper/CDs can be predicted easily. If anyone's worried about the lifespan of CDs, it's always possible to copy the collection once every few years. Also I think that paper could be a viable backup solution, at least for e.g. family photos -- print, encapsulate, hide in a dark and dry place.
    - poikroequ 2y ago
      Are hard drives such a terrible solution? Setup a RAID5 or RAID6 array and you could easily backup thousands of DVDs for less than $1000.
      - stavros 2y ago
        For around five years, sure.
        poikroequ 2y ago
        I have hard drives which are 15 years old that still work just fine. Yeah, hard drives do fail, that's why you use RAID5 or RAID6. 8TB HDDs can be had for around $100 each. Four of these in RAID5 gives you 24TB. That's enough to backup 5000 DVDs (single layer) or 2800 dual layer DVDs.
        stavros 2y ago
        I have a NAS with four drives, I had to replace all four of them 5-7 years later. You must be very lucky if your drives work 15 years later.
        buran77 2y ago
        stavros, to understand if any precautionary measure is effective you must first understand what you're protecting yourself against. Your line of argumentation is moving the goalposts a lot and punctuating each stop with "that's not good". Between the lines I take it you're aiming for "perfect" or at the very least "absolute best" protection. The first doesn't exist, the second is only interesting for only very few. If you're protecting your data from minor damage and decay of the DVD that stores it, having an ECC file stored elsewhere (a newer DVD, or HDD, or cloud) is the lowest effort and cost option but still a big step forward in resilience. It doesn't matter how long each medium lasts, all that matters is that they don't fail at the same time. Pick your HDDs from different manufacturers, models, or batches and the chance that all fail within the same short time period without external influence are exceptionally low. And when one does fail you replace it. You'll never get a one time perfect solution, you're just buying time to rebuild your resilience when you take a hit. If you're protecting against the complete destruction of the disk then an ECC file won't do, you'll need a full copy. Or multiple copies, and in multiple locations. Or on different mediums with very different reliability curves. You might want to protect against internal or external malicious actions, technical obsolescence of the medium or data format, vendor lock-in, or political instability. No one size fits all solution, certainly not a cost conscious one.
account42 2y ago
Beware that GNU ddrescue and dd_rescue are different tools but both are sometimes referred to as simply ddrescue. You almost certainly want the GNU version.
tripflag 2y ago
One trick not mentioned in the article is to repeat the ddrescue with the same CD in different drives; this almost entirely saved my unreadable CDs, as no single drive could read them entirely. My biggest savior was a Pioneer BDR-AD07BK which managed to read some discs that other drives couldn't even get the TOC off! I wrote a gnu-ddrescue wrapper back then to avoid accidentally resuming a read to the wrong iso (only ever tested on alpine): https://github.com/9001/usr-local-bin/blob/master/miso https://github.com/9001/usr-local-bin/blob/master/miso
aidenn0 2y ago
So, I ripped all of my DVDs recently to use on a HTPC, and I ran into about 3 discs that could not be read, but would play in a DVD player. I checked and they do not appear to be discs that are known to have any fancy copy protection. I ran ddrescue on two different DVD drives and a blu-ray drive, up to the point where 48 hours would pass with no new data recovered. This left me with still several minutes of video that was unwatchable. I solved it by spending about $12 to get used copies of all 3, which ripped fine. Any idea(s) that I could try had that option not been available?
Lammy 2y ago
The most important preventative measure in my experience: don't lay CDs upside-down in the name of “““protecting””” them! I know it's counter-intuitive, because I used to do it myself, but take a look at a cross-section of a CD and you'll see why it's the worst possible thing you can inadvertently do. The data layer is directly under the label, and the bottom of the disc is relatively well-protected in comparison: https://www.clir.org/wp-content/uploads/sites/6/fig2-3.jpg https://www.clir.org/wp-content/uploads/sites/6/fig2-3.jpg This is also the reason why all-over-print CDs are better survivors than discs whose obverse design integrates the raw silver. Note that this is specific to CDs — DVDs and BDs have protection on both sides!
wkat4242 2y ago
There used to be a pioneer drive you could flash with replacement firmware that could read raw data (even the ECC!). I used to have one of those but lost it in a move :'( It was really handy to get scraps off a disc that was very damaged.

93 points by nixass 2y ago

https://archive.is/djjCY https://archive.is/djjCY Wasn't able to easily decline cookies.

> Dvdisaster can be used to generate error correction code files for an optical disc, which is in good condition. We should then store this ECC file in a safe place. Can't store some data reliably for a long time? You can mitigate it by storing some other data reliably for a long time.

buran77 2y ago
If you already have a lot of data on older, less reliable storage formats you have the choice of keeping a full copy all that data on something with higher reliability, or store just a small fraction of it in the form of the ECC file. The first option may be technically more sound but comes with a larger investment in terms of time and money. Second option may be less reliable but with significant savings. It's up to the owner of the data to decide how to balance these.
- stavros 2y ago
  What sort of higher-reliability options (than a Blu-ray) does a consumer have? I struggle to think of something that's not fairly niche, eg a magnetic tape drive.
  - buran77 2y ago
    > higher-reliability options You'd be comparing to an old optical disc. So almost anything is higher reliability than that, starting with a newer optical disc and probably ending at any cloud storage. > does a consumer have This isn't limited just to your average consumer. DVDs are still in use in libraries and different archives which can't afford to store a full backup. We've had parity checks appended to the very same data to be protected for so long because it does protect from some common failure modes even if not from all. Dvdisaster goes one step beyond and gives the option to store the ECC file elsewhere. Definitely better than nothing and probably even with a very good cost/benefit ratio.
    - self_awareness 2y ago
      buran77 wrote: > You'd be comparing to an old optical disc. So almost anything is higher > reliability than that, starting with a newer optical disc and probably ending > at any cloud storage. Is "cloud" really being considered as a viable backup solution? I mean, some of my CDs are older than most of today's "cloud" servers and can be read just fine.
      - buran77 2y ago
        > some of my CDs are older than most of today's "cloud" servers and can be read just fine. And if you're happy being able to recover "some" of your data that's a perfectly legitimate option. Write CDs and DVDs, save to HDDs and SSDs, to the cloud, print on paper, or a combination of all. Only you know your data and its importance. But what you'll want to ask yourself though is how many CDs written since than can't be read just fine. I have books from before electricity was a thing and still am thoroughly convinced paper is not the best for long term preservation. My oldest cloud stored data that I can verify is a 25 year old email in my Yahoo mailbox. I have stamped CDs that survived that long, no written CD that I can think of.
        self_awareness 2y ago
        Well, Yahoo is one of the few e-mail providers that survived the last 25 years. I had e-mails on multiple providers which don't exist since a long time. That brings another question, how do you even know that the cloud company will even exist in the next 25 years? I think Yahoo is now enforcing OAuth authorization. Maybe next step is to remove IMAP? How do you know that they're not planning it? The point is that it's impossible to try and predict how the cloud will look like in the future. One day we can end up receiving an e-mail that we need to download all data from the cloud because they're ending their operation. And the future of paper/CDs can be predicted easily. If anyone's worried about the lifespan of CDs, it's always possible to copy the collection once every few years. Also I think that paper could be a viable backup solution, at least for e.g. family photos -- print, encapsulate, hide in a dark and dry place.
  - poikroequ 2y ago
    Are hard drives such a terrible solution? Setup a RAID5 or RAID6 array and you could easily backup thousands of DVDs for less than $1000.
    - stavros 2y ago
      For around five years, sure.
      - poikroequ 2y ago
        I have hard drives which are 15 years old that still work just fine. Yeah, hard drives do fail, that's why you use RAID5 or RAID6. 8TB HDDs can be had for around $100 each. Four of these in RAID5 gives you 24TB. That's enough to backup 5000 DVDs (single layer) or 2800 dual layer DVDs.
        stavros 2y ago
        I have a NAS with four drives, I had to replace all four of them 5-7 years later. You must be very lucky if your drives work 15 years later.
        buran77 2y ago
        stavros, to understand if any precautionary measure is effective you must first understand what you're protecting yourself against. Your line of argumentation is moving the goalposts a lot and punctuating each stop with "that's not good". Between the lines I take it you're aiming for "perfect" or at the very least "absolute best" protection. The first doesn't exist, the second is only interesting for only very few. If you're protecting your data from minor damage and decay of the DVD that stores it, having an ECC file stored elsewhere (a newer DVD, or HDD, or cloud) is the lowest effort and cost option but still a big step forward in resilience. It doesn't matter how long each medium lasts, all that matters is that they don't fail at the same time. Pick your HDDs from different manufacturers, models, or batches and the chance that all fail within the same short time period without external influence are exceptionally low. And when one does fail you replace it. You'll never get a one time perfect solution, you're just buying time to rebuild your resilience when you take a hit. If you're protecting against the complete destruction of the disk then an ECC file won't do, you'll need a full copy. Or multiple copies, and in multiple locations. Or on different mediums with very different reliability curves. You might want to protect against internal or external malicious actions, technical obsolescence of the medium or data format, vendor lock-in, or political instability. No one size fits all solution, certainly not a cost conscious one.

account42 2y ago

Beware that GNU ddrescue and dd_rescue are different tools but both are sometimes referred to as simply ddrescue. You almost certainly want the GNU version.

tripflag 2y ago

One trick not mentioned in the article is to repeat the ddrescue with the same CD in different drives; this almost entirely saved my unreadable CDs, as no single drive could read them entirely. My biggest savior was a Pioneer BDR-AD07BK which managed to read some discs that other drives couldn't even get the TOC off! I wrote a gnu-ddrescue wrapper back then to avoid accidentally resuming a read to the wrong iso (only ever tested on alpine): https://github.com/9001/usr-local-bin/blob/master/miso https://github.com/9001/usr-local-bin/blob/master/miso

aidenn0 2y ago

So, I ripped all of my DVDs recently to use on a HTPC, and I ran into about 3 discs that could not be read, but would play in a DVD player. I checked and they do not appear to be discs that are known to have any fancy copy protection. I ran ddrescue on two different DVD drives and a blu-ray drive, up to the point where 48 hours would pass with no new data recovered. This left me with still several minutes of video that was unwatchable. I solved it by spending about $12 to get used copies of all 3, which ripped fine. Any idea(s) that I could try had that option not been available?

Lammy 2y ago

The most important preventative measure in my experience: don't lay CDs upside-down in the name of “““protecting””” them! I know it's counter-intuitive, because I used to do it myself, but take a look at a cross-section of a CD and you'll see why it's the worst possible thing you can inadvertently do. The data layer is directly under the label, and the bottom of the disc is relatively well-protected in comparison: https://www.clir.org/wp-content/uploads/sites/6/fig2-3.jpg https://www.clir.org/wp-content/uploads/sites/6/fig2-3.jpg This is also the reason why all-over-print CDs are better survivors than discs whose obverse design integrates the raw silver. Note that this is specific to CDs — DVDs and BDs have protection on both sides!

wkat4242 2y ago

There used to be a pioneer drive you could flash with replacement firmware that could read raw data (even the ECC!). I used to have one of those but lost it in a move :'( It was really handy to get scraps off a disc that was very damaged.