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Data Storage Media

How To Verify CD-R Data Retention Over Time? 303

Posted by CmdrTaco
from the saving-boobies-for-future-generations dept.
Peter (Professor) Fo writes "I've recently had two CD-Rs reported to me as faulty which are just 3 years old. This is worrying — I suspect the failure rate for this batch could be 10%. When researching CD longevity there is old and unreliable information; pious 'how to cosset your discs so they last 100 years' blurb; and endless discussions of what sort of dye to use, don't use cheap media, burn slower (or don't), but not much by way of hard facts besides there's a lot of data loss going on. Does anyone know of a generic utility (win or *nix would suit me) that can map sector readability/error rates of CDs? I'd like to measure decay over time in my environment with my media and my other variables; and I expect others would too."
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How To Verify CD-R Data Retention Over Time?

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  • dvdisaster (Score:5, Informative)

    by Anonymous Coward on Thursday November 06, 2008 @12:32PM (#25662633)

    You should probably try dvdisaster [dvdisaster.net]. it can test media, and can create (on disk or external) redundancy data, which can be used to recover later.
    It's also open source, so you could probably coerce it to export some more information

    • Re:dvdisaster (Score:5, Informative)

      by dougmc (70836) <dougmc+slashdot@frenzied.us> on Thursday November 06, 2008 @02:12PM (#25664181) Homepage
      Very nice. I use par2 [sourceforge.net] for basically the same purpose. I save about 10% of my DVD capacity, and have a program that creates a directory with md5sums of every file, along with par2 files for all the files, so I can recover from a loss of almost up to 10% of the disk's data.

      Of course, if the data lost is in the catalog so I can't even find my files, then things get much more complicated. But even so, I've had to use this system a few times (due to damaged DVDs mostly) and it's worked pretty well.

    • Re:dvdisaster (Score:5, Insightful)

      by iamhassi (659463) on Thursday November 06, 2008 @02:43PM (#25664591) Journal
      "You should probably try dvdisaster..."

      Stupid question, but why is the poster still using CDs for data? Hard drives are down to 10 cents per gigabyte, so why would anyone take the time and data risk to still burn information to CDs? I'm slowly moving away from even DVDs.
      • Re: (Score:3, Insightful)

        by Dominican (67865)

        One reason to still use CD/DVD is to easily keep different copies of a file with reduced risk of ALL data getting lost at once.

        A HD may easily become a single point of failure.
        Example:
        Say you have 2 drives.
        Drive A - Current data
        Drive B - Backup data with multiple versions.

        If drive B dies you potentially loose all your backups at ONCE.

        For very important files a combo of HD and CD/DVD (or a cloud service) probably produces the best protection with relatively ease of maintenance.

      • Re: (Score:3, Informative)

        by hansamurai (907719)

        10 cents is pushing it, I'd say more around 13 cents per gigabyte, but DVD media sits happily at 5-6 cents a gigabyte. Of course there are obvious differences, but my mantra is "burn and forget." I don't need to be bothered taking up hard drive space for a movie or iso I may need once a year. I just file the disc away in a large stack and fish it out if I ever need it.

        Though as hard drives continue to fall in price and media stagnates (at least this generation), I will probably eventually buy a very larg

      • Re: (Score:3, Insightful)

        by MinutiaeMan (681498)

        Stupid question, but why is the poster still using CDs for data? Hard drives are down to 10 cents per gigabyte

        Are you serious? CDs are a useful way to distribute a large group of files through a method other than e-mail (or "the cloud," though I kinda hate that term). It's especially helpful if the information needs to be available for a while... That is, rather than storing the files somewhere on a server where things can get lost or moved, sometimes having a physical CD is just a better option.

        By you

  • by asc99c (938635)

    Nero has a test utility, but I've not really found the results to be all that useful.

    I get similar results from both unreadable discs that are 8 years old and stuff that I think is high quality Verbatim discs burned this year.

  • by Phizzle (1109923) on Thursday November 06, 2008 @12:34PM (#25662655) Homepage
    Archival Grade Media makes a HUGE difference for backing up important data. It is not very expensive and widely available.
    • by Kamokazi (1080091) on Thursday November 06, 2008 @01:26PM (#25663575)
      Also looking for Taiyo Yuden brand helps (or anything made in Japan...that should be TY just rebranded). Every knowledgable board I've looked over on the subject has recommended them, and I have never had a single one of their disks out of probably 200 now be bad from the start. Unfortunately I don't have any 'old' disks to test. I keep most of my data backed up on hard drives.
      • Re: (Score:2, Interesting)

        by n1ckml007 (683046)
        Does TY make DL discs?
      • by Penguinoflight (517245) on Thursday November 06, 2008 @02:09PM (#25664143) Homepage Journal

        Taiyo Yuden is excellent media, as is most Verbatim media.

        To answer a sibling question: no, Taiyo Yuden doesn't make dual layer discs. Verbatim does, but they aren't up to the quality of their single-layer discs.

    • by Lumpy (12016) on Thursday November 06, 2008 @02:12PM (#25664179) Homepage

      Exactly. I have 60 archival grade CD-R
      s from over 10 years ago that are still readable Yes I have tried them, it is a part of our backup integrity testing every year.

      Storage and handling is also very important with them as well.

    • Re: (Score:3, Insightful)

      by rescue me (1067874)

      Archival Grade Media makes a HUGE difference for backing up important data. It is not very expensive and widely available.

      Do you have any proof that the media makes a difference ? I recommend covering them in honey so that they stay sweet for 100 years.

    • DVD-RAM too (Score:5, Interesting)

      by LinuxGeek (6139) * <djand.nc@gmLISPail.com minus language> on Thursday November 06, 2008 @02:21PM (#25664305)

      I use dvd-ram [wikipedia.org] to archive important files. Designed for archival type storage, the slower media has a 30 year designed life, the faster media has something like 5 year. Add in the builtin ecc and cheap cost, it is a good way to save my source code and photos.

  • CDCheck (Score:2, Interesting)

    by Anonymous Coward

    http://www.kvipu.com/CDCheck/

    Create a CRC file for the CD. Saved me more than once.

  • par2 (Score:5, Informative)

    by Drinking Bleach (975757) on Thursday November 06, 2008 @12:35PM (#25662691)
    Whenever I back up important data, I use par2. If the disc has I/O errors, I just make a full image with dd_rescue (skips past bad blocks, whereas dd will just halt operation) and run "par2 verify" on it. If it's really important, I always verify the integrity no matter what (I've even done it on discs 2 days old, and sometimes, due to the reliability of CD/DVD-R media, it even has errors to repair).
    • Re:par2 (Score:5, Interesting)

      by Waffle Iron (339739) on Thursday November 06, 2008 @12:51PM (#25662991)

      If it's really important, I always verify the integrity no matter what

      I do that even if it's not important. I have a script which creates an md5 checksum file for a directory tree and adds it to the directory, and I always run it before burning a CD or DVD. Once burned, I verify the checksum on two different computers.

      There have been a few times that the computer that burned the disc successfully verified a new disc, but a different one didn't. When that has happened, I trashed that disc and made a new one.

      Sometimes I wonder if a lot of the reports of "deteriorating discs" are actually cases where someone burned a coaster in the first place, and just never happened to try to read or verify the data until years later.

      • by xaxa (988988)

        I do the same, except I don't have a script to make checksums for a directory tree, as it's a one-liner with Zsh:

        md5sum **/*(.) > Checksums.md5

        The (.) restricts the match to only normal files, the ** specifies a recursive match.

        • Re:par2 (Score:5, Insightful)

          by Drinking Bleach (975757) on Thursday November 06, 2008 @01:22PM (#25663529)
          The problem with md5, is that it does nothing to repair broken data. It's great when you download something and find out it's bad so you try again, but for long-term data storage, knowing that your data is corrupt doesn't do you a whole lot of good. Which is why I recommended par2, it can both verify and (more importantly) repair data.
    • Re:par2 (Score:4, Insightful)

      by Fast Thick Pants (1081517) <fastthickpants@@@gmail...com> on Thursday November 06, 2008 @01:54PM (#25663937)

      I've used par2 for this purpose, and it's not bad. It doesn't support multiple directories -- you have to create separate parity data for each directory on the CD. It also has no support for restoring any filesystem metadata, only the file names and contents.

      I've also used dvdisaster, and I think it has some advantages. It creates a single block of error correction from the entire disc image, so it includes any filesystem information on the disc. It can use existing media in the drive, or an .iso file. The error correction data can then be appended to the .iso file before burning (assuming you've calculated the size correctly.)

      I'd really like to see dvdistater's method become a standard feature of CD burning software, with the presumption that most people would want to add error correction to their discs if there's free space. Operating systems could check for this data when reading a CD and automatically use it to detect and correct read errors.

      I'd really love to see this system adopted by software companies, music labels and movie studios -- but of course they'd much rather have a shot at selling you another copy of the disc you scratched.

    • Re:par2 (Score:4, Informative)

      by zippthorne (748122) on Thursday November 06, 2008 @02:00PM (#25664015) Journal

      Problem with par2 is that it does not work well with lots of files spread out across directories, and it especially doesn't work recursively. Though par2-ing your image is still probably a pretty good idea.

      My partial solution so far is to make a hidden directory and hard link *every* file on the disk into that directory, then run par2 in that "flat" directory. (I put the inode number in the filenames to make sure there aren't any name collisions. If you use the inode number AS the name, you won't get any dupes on multiply linked files)

      I haven't got the details worked out yet, though, but iso9660 supports hard links, so the disk burns and verifies well, and (importantly to me) unlike dvdisaster, it's not just a technically usable image, but an actually standard-compliant image.

      I'm not quite sure how I'll go about restoring if verify fails, though, since the goal is to keep the same directory structure (presuming it's still mostly intact) and repair the files themselves. Perhaps unionfs over the loopback mounted iso would work. Or just repairing the files and using the a recursive directory listing (also saved on disk) to regenerate the directory structure.

      But this would all be less necessary if the standard ECC in the CD format was more generalized: i.e. you could set it to always use the entire disk, no matter how little actual data you had, and just use extra layers of ECC that take advantage of the extra space. It would be good if reading could still be done transparently (like current CD ECC) and report "goodness" of the disk as determined by how much of the parity data was actually needed (so you could keep track of degradation over time, if any, and replace disks if the numbers start increasing)

    • by fizzup (788545)

      Three questions:

      What redundancy percentage do you use for the par2 recovery files?

      Have you ever successfully recovered a borked cd or dvd?

      Have you ever tried & failed to recover a borked cd or dvd?

  • by MarkoNo5 (139955) <MarkovanDooren@noSPAm.gmail.com> on Thursday November 06, 2008 @12:36PM (#25662695)
    The following tool allows you to track the failure rate of your media, and allows you to recover the files and replace the cd/dvd when it starts failing. http://hardware.slashdot.org/article.pl?sid=08/08/03/197254 [slashdot.org]
  • And suggest that instead of using CD-R's anymore, you buy some 1TB portable drives and keep them backed up. I don't know your application and you don't explain it, so this is more of a statement about how crap CD-R's are for archiving anything at all, ever. If you have important data on a CD-R, back it up asap.

    • Mod parent up! (Score:5, Insightful)

      by GroundBounce (20126) on Thursday November 06, 2008 @01:08PM (#25663285)

      I have many gigs of digital photos and I have also more-or-less moved away from optical media for backup and switched to HDD. As the original poster mentioned, most of the "information" you find on the net about archival longevity of optical media is personal anecdotes or pet theories, and good hard data on archival longevity of CD-R or DVD+-R is hard to find. My own personal experience is that name brand discs do have fewer problems than cheap "house brands", but it's hard to quantify or say much beyond that.

      Backing up to hard drives has a number of advantages:

      1. It's a heck of a lot easier - in most cases of personal data backup, a few 1TB HDDs will hold all the data you need to back up, so there's no need to manage boxes of 100's of discs. I usually back up the same data onto two HDDs, and store one of them in a firesafe. If you're really worried, you can store one of them offsite.

      2. Since no media will last forever, you will *always* need to roll your data over to new media every so many years. With HDDs, its *much* easier to roll your data over to new media every 5 or 6 years. Think of transferring two or three HDD's to a new HDD (by the time you roll over the data, the new HDD will probably hold all the data from those two or three older HDDs), compared to re-organizing and re-burning hundreds (or more) of CDs or DVDs.

      The bottom line is that if a few HDDs don't hold enough data for your needs, then backing up to optical media will be totally out of the question anyway, and you will probably need to use tape.

      • Re: (Score:3, Informative)

        by painandgreed (692585)
        3. An external back up HDD or three will fit in a fairly small safety deposit box, so you can recover your data if your house burnsdown or is robbed. A similar number of CDs or even DVDs would require a much larger box to do so and is easier to manage.
    • by g253 (855070)
      Oh gosh, not again. This is the same as suggesting to install Ubuntu when someone has a windows-related issue.

      Once and for all : the answer to "how to make FOO work better for me" is not "you should use BAR instead"!
    • by Paralizer (792155)
      Use tapes, hard drives fail all the time. Or you could get a nice NAS with a bunch of hdd's in some ultra redundant RAID configuration. Personally I would go with the NAS, but now you're getting into the couple hundred dollars range and it's not as portable as CD-R's or tapes.

      Backing up from one hdd to another is a silly idea. If that's the most viable solution for you you might as well go RAID-1 so at least you always have a mirrored copy (I do this on my home machine and it works fine for me).
      • by quanticle (843097)

        Well, hard drive failure is only an issue if the hard drive is on and spinning. If you just hook up the drive when you backup, and power it off afterwards, then isn't better than burning to CDs every so often?

        I guess it comes down to how long hard drives hold data as opposed to CDs.

  • by Maxwell42 (594898) <olivier DOT jaquemet AT gmail DOT com> on Thursday November 06, 2008 @12:40PM (#25662765)

    If you consider your data worth it, have enough time and enough money, you should probably re-burn/re-save them to long lasting media.

    There was a previous post on askslashdot about this subject.
    http://ask.slashdot.org/article.pl?sid=08/08/27/2119252 [slashdot.org]

    My suggestion was to use Plasmon "Century-Disc" :
    http://slashdot.org/comments.pl?sid=914095&cid=24784787 [slashdot.org]
    (even though I have never tried it myself)

  • Nero has various tools that might be useful. I'm not really into this sort of thing as the people who are into it are generally off the deep end and take it way too seriously. The CD-R Freaks website might have some people who have helpful suggestions.

    I have CD-Rs that are 7 years old that still work. In fact, I've never found a failure. You might consider using PAR to make PAR2 files for your CD-Rs so you can recover the data if it's important to you. You'll need to make those PAR2 files at the tim
  • If you have a high failure rate then its because you are using crappy media. Just like buying heaper casette tapes strethed faster than the more expensive, the cheaper the media, the less reliable its going to be. Unless you plan on continually verify disks randomly I don't really understand the point of testing the media other than to generate some useless numbers. Call a company, find the one with the best actual rating for your price and refresh every 75% of that. I guess its conceivable that certain bur
  • by kcdoodle (754976) on Thursday November 06, 2008 @12:40PM (#25662777)
    Never, ever had a CD die on me due to old age. I have burnt CDs that are probably older than you.

    The only 2 reasons I have ever had a CD die.
    1. Bad burn.
    2. Dropped it/scratched it.

    Okay, I really have only had one reason CDs die:
    1. I can be somewhat of a dumb-ass.
    • by xaxa (988988)

      Never, ever had a CD die on me due to old age. I have burnt CDs that are probably older than you.

      Wow, I feel old -- is the average age that low round here?

  • Add PAR2 files (Score:2, Informative)

    by Still an AC (1390693)
    When archiving data to CD or DVD I use a program call Quick Par [quickpar.org.uk] to generate recovery files that I can use to repair the data on the disc if it becomes damaged.
    It is based on the same recovery tech that RAID systems w/ parity drives use, and is mostly used to repair Usenet downloads. I usually put 4GB of data and 400MB of PAR2 recovery files on the disc. This will allow ~10% data loss before recovery is not possible. Also I dont have to worry about the TrueCrypt vol becoming damaged and unusable as well
  • by Wanker (17907) * on Thursday November 06, 2008 @12:44PM (#25662865)

    The obsessed people at CDFreaks can help. Here's a link to their FAQ on CD-R media:

    http://club.cdfreaks.com/f33/media-faq-61943/ [cdfreaks.com]

    In other places in the cdfreaks forums, you'll find links to tools that can read the C1/C2 error rates. One of the simplest is "readcd", part of the "cdrecord" programs on Linux.

    In the DVD world, Lite-On and Plextor both make proprietary programs to read the media-level error rates which only work with their own drives. Lite-On has a Linux version of theirs.

    • Re: (Score:2, Informative)

      by Opyros (1153335)
      Note that on Debian-derived distros, the equivalent of "readcd" is called "readom".
  • Tape (Score:3, Interesting)

    by sexconker (1179573) on Thursday November 06, 2008 @12:46PM (#25662899)

    Backups? Use tape.

    Optical media is inherently shitty.

    If you want to get the best out of it:
    Buy good media.
    Burn at a slower speed.
    Verify the data after burning it.
    Store it well. A hard case, and a cool, dry location away from the sun are all you really need.

    If you want to test the quality of a disc, go ahead and use any of the tools recommended here.

    If you want to harden your discs, go ahead and use any of the CRC tools recommended here.

    But really, you shouldn't be using optical media as anything other than a cheap delivery medium. If you need to send stuff to people and you need them to have a copy of it indefinitely, tell them to make a damned copy of it, or give them 2 copies, or keep an ISO and send them a copy when theirs fails.

    • Re: (Score:3, Insightful)

      by rho (6063)

      Tape isn't better than optical, necessarily. All backup mediums require testing to ensure reliability, which generally means restoring from backup.

      If your data is critical, keep it in several places at the same time, and as closely synced as you can manage. Hard drive, mirrored to another hard drive, backed up to an external hard drive, swap out external drive for another every week (stored off-site), run incremental backups to tape nightly, use an online backup service like rsync.net or Carbonite. Even t

  • Professional Advice (Score:5, Informative)

    by polyomninym (648843) on Thursday November 06, 2008 @12:48PM (#25662937)
    I work with CD/DVD and related technology as a profession. I analyze, QC, and mass duplicate media by the thousands for extreme and critical field use, every day. My best advice to you is to use Taiyo-Yuden (TY) media, always. I've seen mixed results and bad burns from Mitsui and MAM-A gold, Kodak, and the like. The TY dye type has a proven longer longevity than any other so far. I also suggest burning all of your audio CD's at 16X, this affect what's called single-beam readers. Also, it insures higher integrity of the burn. Burn 16X DVD's at 8X to increase the write integrity.

    What others say about is CDCheck is true, use it along with this advice. Use Plextools Pro on a PX-716 drive if you can find one. It seems to be more accurate than Nero tools. Use Plextools to check the C1, C2, and CU rates. If the graph is half-way to the top of the reading, back that disc up. As cheap as media is, I suggest burning more than one copy, storing the image on an external archive hardrive. When burning, don't use overburning. You lose some integrity for error correction.

    Store your media in a cool dry place, on it's side. Avoid humidity, light, and heat when you can. Remember, the best analysis tools in the industry are very expensive for individuals. Take a look at CATs if you are interested in learning more about optical media testing. Best wishes!
    • Taiyo-yuden media is not labeled as such. What brands are consistently made by TY?
      • by AxemRed (755470) on Thursday November 06, 2008 @01:36PM (#25663681)
        You can buy Taiyo-Yuden media at...

        http://www.supermediastore.com/ [supermediastore.com]

        That's where I got mine. I haven't had a bad burn yet.
      • by mobby_6kl (668092)

        Some of Verbatim DVD+Rs (and probably CD-Rs too, but I haven't used those in a few years) are actually made by TY, some of their other ones are Mitsubishi Chemical (Verbatim's parent company), which in my experience are also very good. Some types were also made by other OEMs which are supposedly not as good, but I haven't had any problems with any of the Verbatim branded media. Of course, if you look around you can find TY branded media as well, like at the places mentioned in the other two posts.

    • I also suggest burning all of your audio CD's at 16X

      Did you mean 16X, or "16X or slower"? So-called 52X recorders start at about 20X and reach 52X when they reach the outside of the disc with a greater linear velocity. Forcing 16X makes the recorder use a constant linear velocity over the whole disc to minimize the effects of vibration. But is there anything special about 16X that makes it better than 12X?

      this affect what's called single-beam readers.

      I just wanted to add something to help people understand what your post means. In cheap mechanisms, used in cheap CDDA players, the pickup moves the laser

      • by Scaba (183684)

        Learn more about pickup strategies

        Finally, the secret of how to meet girls! Oh, wait...

    • I have seen bad CD burns from Mitsui Gold, usually on a burner that is not working particularly well or on blank media that is a bit old. However I have never (7 years now) had a Mitsui Gold CD go bad on me in storage.

  • use CD/DVD speed (Score:5, Informative)

    by YesIAmAScript (886271) on Thursday November 06, 2008 @12:48PM (#25662939)

    http://www.cdspeed2000.com/ [cdspeed2000.com]

    You need certain brands of optical drives, but with them and this program (and others), you can see the PI/PO or C1/C2 correction (I can't remember which is for CD and which is for DVD) rates on a per-sector basis on your disc. As the rates rise, the disc is going bad, becoming marginally readable and you can copy the disc before it becomes unreadable.

    You can find out which drives to buy at http://cdfreaks.com/ [cdfreaks.com]. The terminology on there for a drive that can do this is a "scanning drive".

    I have no idea if you will find that your correction rates are rising over time.

    • Re: (Score:3, Informative)

      by sricetx (806767)
      FYI - Nero CD Speed version 4.7.7.16 runs fine in Linux under recent versions of Wine. The newer version (callled Disc Speed, not CD Speed) does not work under Wine.

      I've used it with two different Liteon SATA drives: a Liteon 20A3S and a Liteon 20A1L. Both of these drives (and I believe, Plextors) support scanning for jitter. When you run CDSpeed, the test you want is the Disc Quality tab. Click Advanced and then check the DVD Jitter checkbox. This test will give a good an indication of the quality of
  • Are you sure that the discs really did burn correctly 3 years ago? Some burning software, Windows I'm looking at you, doesn't report errors correctly.

    For stuff I care about, I always have Nero verify the data when done burning.

  • .sfv verification might be helpful.

    I'm not sure what utilities are available on *nix, but winsfv has always worked for me.

    Generates a checksum file by file, and then dumps the checksums into a file. Simple, fast, and works great.

    I know there are .sfv shell scripts all over the web, as I used to use them on my ftp sites, to verify the integrity of files transferred against the list of checksums. Files didn't match checksum, files automagically deleted.

    When making up your disk images, you could .sfv checksu

    • by JustNiz (692889)

      Thats too high-level. The utility you mention only scans files, meaning degradation in unused or 'system' areas of the CD wouldn't get reported. Also, it only reports errors after any lower-level error-recovery strategy has failed. Consequently it does a good job of hiding actual disk degradation.

      The type of utility that is needed to give an accurate, unaffected report of degradation is a whole-disk scan that reports errors even before any error-recovery strategy is attempted.

  • CD-Rs have a shorter lifespan from mass produced CDs due to different manufacturing techniques. Mass produced CDs last much, much longer. I have CDs that are 15-20 years old and still are perfectly fine. Regular CDs are mass produced by stamping a pattern into a layer in the CD, this yields something much more reliable than the burn in used in CD-Rs. the average age of CD-R is 3-5 years it seems. CDs can last for decades, maybe even centuries.

  • http://qpxtool.sourceforge.net [sourceforge.net] - Linux program for performing low-level quality measurements on CDs and DVDs. It only works with some drive models, so check the supported hardware list.

  • by Phizzle (1109923) on Thursday November 06, 2008 @01:11PM (#25663343) Homepage
    Take a page from the book of Church© of© Scientology©®(TM) and engrave your data on Titanium© Plates© and store it in Gold© Vault©. I apologize in advance to the Church© of© Scientology©®(TM) if I didnt use enough Copyright©®(TM) symbols while referring to Them (©?). Please do not sue me. © (TM) ®
  • I burn 2 copies of everything, an archive, and a "for use". If I start to have trouble with a "for use" disc, then I have two options:

    1) Get my archive disc out, and re-burn a new copy.

    2) Copy whatever files I still care about (some old stuff can die, some can't) to my harddrive, treat as new data, and re-burn on ANOTHER two discs.

    Also, when I RAR anything (backups of dvds or large file repositories, for example), I use the option adds 8 percent parity to the file.

    This is similar to your fancy-schma

  • by Anonymous Coward

    I think that the most reliable way to backup your data is to use a USB hard drive changed every 1/2 years.

    Actually I use two : one at my parents in Europe, one at my place in Canada.

    A hard drive is much more reliable than any CDR/DVDR, and if your data is important it's worth it.

    Just my two cents.

    David

  • What you could do is setup a system that would do the following...

    1. Create a CD and then using your favorite hashing algorithm generate either a whole disk hash or a per sector hash and store this information in a database.

    2. Take a disk out of storage, analyze the disk and if all the hashes match up, use this disk to make a copy. Then rerun step 1 on the second disk to verify that all it's hashes match up and if they do, store both.

    3. Setup up a routine where once a month you pull a volume out of your arc
  • by Godji (957148)
    Several hard disk drives and ZFS (which has automatic error detection and correction). Backup problem solved.
  • When you need storage and reliability for the long term, there's no substitute.

    http://www.historyforkids.org/learn/westasia/literature/cuneiform.jpg
  • I feel that making backup copies using punchcards will ensure that they last a long time. Especially if you can get them associated with an election controversy like the 2000 Florida Election Results. Just make sure that they have hanging chads. :P
  • I use Nero DriveSpeed (I think it's called) to give me a read on sample archived discs from my storage area.

    I have some CD-Rs that are about 13 years old at this point; I wrote them on a 2X writer that the company I work for paid $3000 for - that was the going price at the time.

    Anyway, they're Kodak Gold Datalife discs. I recently pulled 5 samples out of a spindle of 50 discs, and there were only a couple of correctable read errors. This is pretty much what you get on freshly-burned discs too since any li

  • isn't that the dye "degrades" creating error rates. This does happen with CD-RW's and happens really fast. The real problem is the media physically starts to fall off the acrylic and you start getting pinholes where it's missing.

    This phenomena is easily seen by holding the disk up to a bright light. In fact, you'll see these "pinholes" out of the box for some cheap cd's.

    You can use better CD's that are thicker and have a layer of acrylic over the dye layer but the problem then becomes clouding in the clear

  • Different Media (Score:4, Insightful)

    by Plekto (1018050) on Thursday November 06, 2008 @02:13PM (#25664199)

    Sadly to say, the 100 years nonsense is for pressed CDs like you get music and programs on. Burnable ones last maybe 5-10 years, tops. When you add in literal bit-rot due to fungi and so on that exist and love to eat worm-trails in the media surface itself... I've had CDs go bad in as little as a year or two. I constantly have to re-burn my media every couple of years. Thankfully the media density gets better, so I can toss an entire collection of CD-Rs onto 2-3 Blu-Rays and be done with it.

    If you want it to be secure, the only viable solutions seem to be flash media or an old-school hard drive in storage. Thankfully the prices of both are affordable for your critical data. All of my critical data and installers and so on fits in a single 512MB flash drive. Toss that in a safe deposit box and forget about it.

  • CD, DVD Data (Score:3, Interesting)

    by omb (759389) on Thursday November 06, 2008 @03:04PM (#25664919)
    First CD and DVD, including BlueRay, HD, are very different. The CD hardware layer is hugely redundant with each 8-bit byte being written as a 14-bit forward ECC block and each 2048 bit sector is protected by a Cross-interleaved Reed-Solomon code in 304/2048 bits ie hugely redundant. See the Sony/Philips rainbow books.

    Thus unreadability means gross damage, dye decay, scratches or thick dirt. Physical scratches/dirt can often be recovered with very fine metal polish and wash. DVDs are _much_ more iffy. A few readers let you read all the 2352 mode 2 data bits of a data CD but most dont and you cannot detect 14 2 8 bit correction which is the first indication of the dye degrading. If you store the CDs in the dark, in scratch resistant envelopes in a strong box you have a good chance of 20+ years. I wrote the one of the first Philips writer drivers and have CDs that old.

    Otherwise you are down to replication and data washing, but dont throw the washed CDs out!

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