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This process assumes:

1. you have TWO copies of the DVD
2. there MAY be bad sectors on BOTH copies of the DVD
3. the second copy contains the same files (the disk does not need to be an "image copy" of the first, however (the volume labels can be different))
4. you CAN read the directory of BOTH copies
5. you have a copy of Media Doctor or equivalent

Problem: You have files stored on a DVD, when you try and copy them, you get errors, "unable to read file", "bad sector" or similar. Other DVDs work fine. Often, when you try and copy, the copy runs fast at first, then runs slower and slower before aborting with the error message. You find that smaller files are easier to copy.

Cause: This behaviour is due to bad media. The file copies slower and slower as the number of bad sectors on the disk increases, to the point where the drive can no longer read the disk. When this point is reached an error is generated. Prior to this point, the drive is using on-board error correction techniques to recover from errors, this causes it to run slowly. Large files are hard to copy because there is usually at least one bad sector in them.

Solution: Media Doctor has Bad Sector Mapping function, and a Patch File function. Used with two copies of a dead DVD, these functions can be used to recover the data. Use this process:

1. ensure you have enough diskspace to hold all the files on the DVD
2. insert the first copy of the DVD
3. open Media Doctor
4. on the button bar, click Copy CD/DVD, and follow the prompts (this creates a copy of each file on the DVD on your hard disk)
5. wait for copying to finish (this may take days, if the DVD is very badly damaged)
6. remove the first copy of the DVD
7. for each file with bad sectors, make a Bad Sector Map (BSM) file:
   1. select "Create BSM file" from the Remote Recovery menu
   2. click the name of the file to recover, then click Next
   3. type a name for the BSM file (eg. C:\LARGEMOVIE.BSM)
   4. click OK

8. insert the second copy of the DVD
9. for each file with bad sectors, using its BSM file, make a Patch File (SPK) file:
   1. select "Create SPK file" from the Remote Recovery menu
   2. enter the name of the BSM file which belongs to the file to recover (eg. C:\LARGEMOVIE.BSM), and click Next
   3. enter the name of the second copy of the file to recover (eg Z:\LARGEMOVIE.AVI - Z: is your DVD drive), and click Next
   4. type a name for the SPK file (eg. C:\LARGEMOVIE.SPK), and click Next

      Sectors to replace the bad sectors listed in the BSM file will then be copied from the second copy of the DVD, and saved into the SPK file. Once the sectors have been copied, which may take some time (especially if the second copy of the DVD is also damaged), Media Doctor says "Operation Complete", but doesn't give a button to Continue, so we have to close and reopen it to continue.

10. for each file with bad sectors, using its SPK file, apply the patch:
    1. select "Repair file with SPK" from the Remote Recovery menu
    2. click the name of the file to recover, then click Next
    3. locate the correct SPK file (eg. C:\LARGEMOVIE.SPK), click its name, then click Open

       Sectors to replace the bad sectors listed in the BSM file will then be copied from the SPK file, and saved into the copy of the recovered file on your hard disk. Once the sectors have been copied, which is very quick (unless the recovered file had many bad sectors), Media Doctor says "Operation Complete", but doesn't give a button to Continue, so we have to close and reopen it to continue.

Once the patch file has been applied to the recovered file, recovery is complete, you can now copy the file, burn it onto another DVD, or whatever.

Tip: name the BSM and SPK files using the same name as the file you're recovering. Eg. LARGEMOVIE.AVI would have files BSM and SPK files named LARGEMOVIE.BSM and LARGEMOVIE.SPK. Do this so that you do not become confused as to which BSM and SPK files are for which recovered file.

Warning: do not mix up your BSM and SPK files, this will cause incorrect data to be written to your recovered files!

Notes:

• You DO NOT need to be using the same DVD drive or computer to read both DVDs. The directory of each DVD must be readable in at least one DVD drive, however. Also, this repair does not need two DVD drives, a single DVD drive will do.
• Files on damaged CDs can be recovered using an identical process.
• Media Doctor is a sector-by-sector copy program with bad sector mapping and patchfile functionality. Any program that does this can be used in place of Media Doctor.
• This solution WILL NOT WORK if BOTH copies of the DVD have bad sectors in the same place. It works by substituting the bad sectors in the first copy of the file with good sectors from the second copy. If the second copy is also damaged, this is not possible. Media Doctor will recover as many good sectors from the second copy as it can, however, so that the file is left as undamaged as possible. Media Doctor does NOT abort if it has problems reading the second copy of the DVD.
• The recovered file may still be usable, even if the second copy of the file also had bad sectors. Movie and sound files are typically tolerant of a little corruption. If your file is a zipfile, or is raw data, you may need to attempt additional recovery using format-specific tools (eg. a zipfile recovery tool).

Post-mortem: if you ever burn your only copy of a file onto a DVD, ensure to burn TWO DVDs. Recovery using the above process is not possible without two copies. Three copies would be even better, although recovery using three copies would be a complex process. Media Doctor does not provide tools to compare SPKs (eg to see which copy has the least errors), this would need to be done manually, if three copies of the DVD were used.

Background: you may notice patterns or patches in your BSM files, these are due to the damage on the media. A large block of consecutive bad sectors indicates that an area of the disk has failed, perhaps because the manufacturer applied an insufficient amount of coating to that area. Patterns are usually large scratches. One-off errors are small scratches and other miscellaneous damage. If you have patches of bad sectors, you have cheap disks, dump them! They will get more and more unreadable as time passes. There's no point keeping valuable data on cheap media - you may as well delete it now.

Final word: this technique is descended from an old floppy disk recovery technique, if you had two copies of the disk, when the "bad sector" error came up you simply inserted the second copy of the disk and pressed retry. This simplicity is not possible with DVDs as modern operating systems generate an "incorrect media" error if the media is switched while the "bad sector" error message is displayed. Media Doctor's ability to "read through" errors (eg. to continue without aborting when a bad sector is found), combined with its BSM and PSK functions, allow us to switch the media, just as we did with a floppy disk, but we do it at the end of the copy process, not during. This works around the error generated by switching the media mid-copy.

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