[HN Gopher] A Starter's guide on recovering damaged and rotten CDs
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A Starter's guide on recovering damaged and rotten CDs
Author : nixass
Score : 68 points
Date : 2024-08-18 15:21 UTC (1 days ago)
(HTM) web link (secnigma.wordpress.com)
(TXT) w3m dump (secnigma.wordpress.com)
| xnzakg wrote:
| https://archive.is/djjCY
|
| Wasn't able to easily decline cookies.
| stavros wrote:
| > 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 wrote:
| 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 wrote:
| 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 wrote:
| > 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 wrote:
| 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 wrote:
| > 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 wrote:
| 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 wrote:
| 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 wrote:
| For around five years, sure.
| poikroequ wrote:
| 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 wrote:
| 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 wrote:
| 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.
| stavros wrote:
| My use case is my dad (or anyone's dad) backing up family
| photos. It's reasonable to teach my dad to write a few
| CDs, but it's not reasonable to teach him how to
| administrate his own NAS, set up RAIDZ, figure out a way
| to store an ECC file, etc.
|
| For my dad, and anyone just tech-savvy enough to select a
| bunch of files, put a disk in the drive and click "burn",
| the choices are either DVD (which deteriorates) or a
| cloud solution. Anything else is too much, including
| "here's a NAS, it'll last you forever as long as you keep
| it plugged in".
| buran77 wrote:
| But stavros, you started this thread by complaining that
| the solution is bad because in order to protect your data
| you have to create additional data to protect. This is
| the most basic definition of data resilience and misses a
| very critical point: with this in place you only have to
| worry half as much about each data set randomly failing
| (you halved the chance of simultaneous failure, all else
| equal).
|
| Then you moved to the (unsupported) argument that
| consumers don't have reliable options. Then to the
| (unsupported) argument that hard drives fail after 5
| years. Then to the argument that some users are not tech
| savvy enough to use anything more complex than a CD.
|
| The last one is the only realistic yet still relatively
| weak complaint. It doesn't invalidate in any way the
| option proposed in the article. Looking at dvdisaster
| creating an ECC file is at most just as complicated as
| generating the data you're looking to protect. Using a
| commercial cloud storage solution is equally straight
| forward. A consumer friendly NAS is very easy to use
| while not so obvious how to fix in case of failure but
| that's why you're there to set it up and set a sync to
| the cloud(s).
|
| I hope you taught your father how to select appropriate
| quality media blanks, what are the optimum storage
| conditions, how often to check that the data is still
| readable, what to do when a disc becomes unreadable or
| very hard to read, how to replace the optical drive when
| it fails or there's dirt on the lens, and so on.
| onewheeltom wrote:
| There is also the archival quality BluRay M-disc media
| account42 wrote:
| 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 wrote:
| 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
| aidenn0 wrote:
| 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 wrote:
| 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
|
| 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!
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(page generated 2024-08-19 23:02 UTC)