# Is the data on my burned DVD-R recoverable? (Solved - Yes!)

## thmclean

[Solved - See my last post for details.  Short answer, they were only readable from the drive they were burned on.]

A couple of months ago, I used the program scdbackup to make a 39 disc DVD backup of my system.  I checked the first 4 or so DVDs that it burned to make sure that it was actually burning them and that they contained the files they were supposed to.  After that I would check every third or fourth DVD that it burned (it uses growisofs as its DVD burning backend) to make sure that things were going smoothly.  Every disc that I checked looked perfect so I foolishly assumed that the rest were fine as well.

  After a hard disk failure, I just pulled out my stack of backups and was horrified to discover that some of them wouldn't mount under either windows or linux.  Fortunately, I could read the majority of them (thank god I didn't decide to do a rar archive!), but there are about 8 of them that I can't mount, with the error

```
mount: /dev/hdc: can't read superblock
```

   I've seen many other people on the forums complaining about not being able to mount their burned DVDs for various reasons, and I think that my problem is really one of a partially failed burn or unclosed session rather than a hardware issue, because I can read most of the discs perfectly but not others.

  So, my question is:  Is there a way that I can determine if any of the data on these discs is recoverable, and once I know that, how can I get as many files off of the discs and back onto a  hard drive as possible.

  Things that I have tried after reading the forums include:

1)  Mounting the device with 

```
mount -t auto
```

 

```
mount -t udf
```

 or 

```
mount -t iso9660
```

2)  Killing Gnome and X to stop their automounting features and then trying to mount in the terminal.

3)  Installing a hex editor and trying to read the device directly to see if there was actually anything there.

  This one was interesting.  I used biew as the editor and although 

```
biew -a /dev/hdc
```

 didn't show anything in the file at first (0 bytes), when I told it to reload the file from within biew, it showed a filesize of 4294967295 bytes, which is about the average size of each DVD I burned, but the hex editor showed all zeroes as far as I could tell.  I have no clue how to really use a hex editor, but this was what somebody on the forums suggested, and all zeroes doesn't sound promising to me).

4)  Tried to do a block by block copy with 

```
dd if=/dev/hdc of=/tmp/dvdimagefile
```

 but I got an I/O error message.

5) 

```
cat /dev/hdc
```

 or 

```
cat /dev/cdrom
```

 both give I/O errors

  I realize it's not looking good for me, but I'm pretty desperate and motivated to get the data back by any free means necessary.  I'm not going to pay some data recovery company $10,000 to get the data back, but I'm willing to sink a lot of time into it if that's necessary.

  Can anybody help me?Last edited by thmclean on Wed Nov 23, 2005 5:13 pm; edited 2 times in total

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## drwook

To be honest if you're getting i/o errors trying to dd from the device I'd be inclined to think it's the media themselves as filesystem shouldn't come into it...  

You may have limited success telling dd to ignore the errors & loopback mounting the image, can't remember the option and at a windows machine at work atm but 'man dd' or 'dd --help' should tell you it  :Smile:   Even if it does work, don't count on getting everything back.

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## frostschutz

 *thmclean wrote:*   

> A couple of months ago, I used the program scdbackup to make a 39 disc DVD backup of my system.

 

Not a very useful backup, unless you have such huge amounts of static data.

 *thmclean wrote:*   

> I checked the first 4 or so DVDs that it burned to make sure that it was actually burning them and that they contained the files they were supposed to.  After that I would check every third or fourth DVD that it burned (it uses growisofs as its DVD burning backend) to make sure that things were going smoothly.  Every disc that I checked looked perfect so I foolishly assumed that the rest were fine as well.

 

If you want to do it right, you not only have to check wether or not a disc was burned successfully, but also wether the data that was written on the discs is correct (md5sum or 1:1 comparison), and, if your drive supports it, check that the burning quality is acceptable as well. CD/DVD age with time, so on a new disk there should not be too many correctable errors, otherwise your disc may be unreadable in the future.

I prefer redundant backups, for example doing one every week, and keeping backups from the last 3 months. So even if the backup from last week failed for some unknown reason, I can still use the one from the week before.

 *Quote:*   

> 
> 
> ```
> mount: /dev/hdc: can't read superblock
> ```
> ...

 

That sounds very bad. Can you verify wether there was anything written on these discs in the first place? DVD-Rs usually have a slight change in color in the area that was written (compare a disc that is readable with one that is not). If there's nothing written on the disc in first place, there is nothing to rescue and we can stop trying (you'd then have to worry about reconstructing parts of your data from the working discs).

If there's something written on the disc, you'll first have to get at the raw data, using dd with disabled error checking and zero padding options, or dd_rescue (which does about the same). This will give you (parts of) the DVD image, with the unreadable parts (if the disc is damaged) zeroed out. If the disc is damaged, try reading it in another drive. Try it in as many drives as you can get your hands on, actually, as different might be able to read different regions of the disc and thus allowing you to put it all together into one complete image. Cleaning the discs might be an option if there is visible dirt on them, however you have to clean them properly. Cleaning them the wrong way will only make things worse.

When you have the image of a disc on HDD, you can worry about getting it to mount. The 'file' command should hopefully be able to tell you what type of filesystem was burned on the disc; if 'file' just tells you that this is 'data', most likely this means that there was wrong data written on the disc. This is where you actually need hexdump / hexedit to find out what the raw data looks like (or rather, if there is any data at all... if it's 4.7GB of zeroes, there is no data to rescue). Depending on what you find out by looking at the raw data (header, magic numbers, data structure), it might be possible to fix the filesystem and make it mountable. It all depends on what exactly went wrong when burning the disc...

If the filesystem can't be made mountable under any circumstances, it might still be possible to peel some data off the disk (for example, if the disc contained only one big tar file, looking for the tar file header might enable you accessing it, even if the filesystem superblock was damaged).

Hope this helps somehow

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## xepk

Yeah this sounds like bad media to me....cheap DVD-R's have a very short life.  If you want to confirm, check the brand and DiscID of your DVD's.

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## thmclean

Thank you all for your replies!  To respond to some of your comments:

  - According to Nero InfoTool the media are Prodisc 4x DVD-R (single layer), and they aren't readable in either my G4 iBook's combo drive or my Dell laptop's Sony DW-D56A DVD+-RW burner.  I'm away from home and haven't tried the discs in the burner they were created in (BenQ desktop burner, don't remember which model, but I'm sure it could write DVD-R as I burned many others successfully in it).

  - Examination of the burned side of the disc indicates that there was indeed something burned onto the disc (color change over most of the surface), but that there is more unburned surface on the innermost and outermost parts of the problem discs than on the discs that read correctly.  I thought that discs are both read and burned from the center outward, so it is suspicious that the innermost part of the problem disc would have more blank space than the good discs.  

  - Most of the data were static archival stuff with only a few of the discs for the system, and in retrospect I didn't really need the system discs.  If it had worked correctly, scdbackup is a nice tool because it provides an ability to create incremental backups onto universally readable uncompressed or AFIO DVD.

  - I'm in the process of reading up on dd_rescue to see if I can grab any data off of the discs.  

  Thank you for your help so far!

  Tom

----------

## xepk

Prodisc's are usually decent disks (here they are rated as 2nd class, 80-95% success rate).  They certainly aren't the type of discs that I would expect to be unreadable a few months after burning.  Unless you got a really poor batch or they have been damaged since burning in some way, I'd say you can rule out media issues as your root problem.

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## NeddySeagoon

thmclean,

Hmm. DVDs and CDs are burned from almost the centre out, then the catalog is written in the centre when the media is closed, so it sounds like your media is not closed. You should be able to read such disks in a writer but not always a reader.

If it were a multisession CD I would suggest using mount -o session=X ... where X=0 for the first session. Maybe worth a try anyway. See man mount

You may be able to recover the content with isobuster under Windows. Its a free download.

Its also supposed to work under WINE but I've never had any luck with that.

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## thmclean

At an 80% success rate, out of 39 discs, I should expect 7 to 8 bad ones, which is approximately what I have.  It's strange that I had burned many of the same discs before one-at-a-time and never had any problems, but in this marathon burn I started getting more errors.  Maybe my burner got periodically "tired!"  Still reading up on dd-rescue (nice that it's in portage!).

@NeddySeagoon

  I have downloaded and tried IsoBuster under Windows.  It reports a single session containing a single track 4.15GB (4,452,483,072 bytes) in size.  It is unable to recover any directories or files, however.  I tried to extract Track01, but it couldn't read any of the sectors.  Under sector view I get the error message "Device reported Error code 05/21/00"

  -Tom

UPDATE!!  

I can still read the discs on the computer they were burned on!  I don't know if this is a hardware or software dependent issue, but all I know is that my data are recoverable!  

The drive that I used to burn the discs and - as far as I can tell the only one that can read them - is a Lite-On DVD+-RW / CD-RW, and neither the Apple iBook combo drive, nor the Sony DVD writers in my laptop and other desktop machine can read the discs.  But the Lite-On reads them just fine without a hiccup.  Go figure.  I have to say that despite this episode, I've found Lite-On drives to be the most reliable and versatile for the money, and even in this case, I suspect that it was the burning software that created the funky discs in the first place.  Definitely sticking to k3b from now on, but at least I know I'm not crazy that the discs read fine when I checked them in the Lite-On drive immediately after burning.

----------

## Entropy42

Someone else said they had good results with Prodisc discs - I'm going to throw in my opinion at the opposite end of the spectrum.  I bought a batch of Prodisc DVD-RW discs a while ago and they were the absolute second WORST DVD media I have ever used (with Princos, of course, being the worst).

I keep on finding TDK media cheap after rebate at various places, and haven't burned a non-TDK -R in ages.  I haven't had a single -R coaster in as long, although I'm paranoid and burn 8x media at the minimum speed of 4x (8x media doesn't seem to be burnable at any lower speed with my Lite-On drive).  -RWs are a different story, many of my drives don't like them.

DVD recorders in general are known for having some of the best readers, especially Pioneer drives.  Not sure how the Lite-Ons compare, but so far I haven't encountered a disc my Lite-On had any trouble reading.

----------

