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Double-layer DVDs written in data format are unreadable

Lone Bobcat


I have Toast Titanium 6.1.


I normally use the "DVD-ROM (UDF)" setting to burn data DVDs on double layer stock. I have burned and verified many successful data DVDs this way. Then, without my noticing, the default setting in the software got changed to "Mac & PC", but I continued to burn and successfully verify another dozen or so with the new setting, thinking everything was okay.


Recently I tried to read one of these "Mac & PC" discs and discoverd they (all of them) hang the OS X Finder when I try to copy files back out to the hard drive. (The disc mounts successfully and opens to show me the file structure inside, but any attempt to copy a file from the DVD to the hard drive causes the DVD drive to shut down and Finder to hang at the very start of the copy.) I have to do a panic shutdown and reboot to get things running again. (Force Quit does not work.) The UDF format DVDs, on the other hand, read back successfully without any problems at all.


ALL of these DVDs were verified successfully by Toast at the time I created them, so Toast must have some way of reading them back successfully in either format. The OS-X Finder apparently does not, because the "Mac & PC" formatted discs consistently cause the hang.


I have tried reading these discs under both OS X 10.4 on a PowerPC-based machine and under OS X 10.5 on an Intel-based machine. Same failure mode on both.


These discs contain very important data that does not exist elsewhere. Is there some way I can retrieve the files on them?

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I wonder what would happen if they are read by a PC?


Something to try is to choose the Copy window in Toast and choose Save as Disc Image. If that worked you will have a mountable disc image file on the hard drive and I expect no problems copying files from it. You also could try dragging files from the DVD to the Data window and choose Save as Disc Image to try to copy them to the hard drive.


Yours is the first report that I can recall about this issue. Let me know if either of those workarounds are successful. The data is recoverable but we just have to find a method that works.

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Thank you very much for your response. I wasn't sure anybody would even be watching this forum.


I tried both of your ideas, neither of which I had thought of myself. Things looked good at first, but we're not there yet.


The copy function was actually able to read from the DVD, but quit at exactly the half-way mark on the progress meter, (I don't think this is a coincidence - see below) with the message "Couldn't complete the last command because there was an I/O error (your disc may be copy-protected). Result Code = -36".


The data window failed right away, with the message "The file XXX could not be accessed. (Data fork, -36)" when I invoked Save as Disk Image. The Power PC and Intel machines both gave the same results.


In thinking back to how I made these discs, I realize the picture is more complicated than I thought. All of the offending discs were made on the Intel OS X 10.5 machine, because I was having trouble with the machine I normally use (the PowerPC on OS X 10.4). The Intel machine would finish the copy, then hang before Verify could start. I assumed that was due to a minor incompatibility between the newer 10.5 OS and Toast 6, so I used the Compare function in Toast to do the verify. No errors were reported, so I assumed the DVD was okay. Perhaps the hang was the first sign of the problem I'm having now.


Meanwhile, I've made an interesting discovery - I can tell the good discs from the bad simply by looking at them! The bad discs have data out to about the 80% mark - from there to the edge, the disc is blank. The good discs are written fully to the edge, and I can actually see a second layer coming out to about the half way mark. (All the discs in this series have about the same amount of data.) It would appear the two formats used fundamentally different ways of allocating the layers!


Do you know anything about the standards for double-layer DVDRs? Is one of these formats just plain wrong, or do I have a chance of finding software that can read it? (I will be able to try a Windows machine next week when I am in town.)


Sorry this is so lengthy, but I'm appreciating any help you can give.

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I wonder if the data on the second layer is just not there even though the disc's directory is expecting it. I don't recall what Toast 6's limitations were regarding writing data to DL media nor if there are incompatibilities with using Toast 6 with Intel Macs. In any case, what matters is how to get the retrievable data off the disc. Toast 9 and 10 have a Disc Recovery feature in the Copy window that "helps recover files while copying data discs with read errors due to scratches or other damage." That may or may not help. There also are special applications that recover files from damaged discs. One that I have is Data Rescue II.

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I downloaded a demo copy of Data Rescue 3 and gave it a try (took about 12 hours). The result was a list of more than a hundred files, each about 3 mbytes in size. Since the original data included one large (6 gig) video file and a half dozen small ones, it looks like things are pretty chopped up. The demo version allowed me to request one of the files to be recovered. I chose one at random and got a 2-3 second video clip I was actually able to play in Quicktime. There was no sound, but sure enough it was a piece of video I recognized. So, as we both suspected, (at least some of) the data is there, but it's badly fragmented, and this particular recovery program is not going to be able to put it back together. I will still try a windows machine (also Toast 9 or 10 if I can find someone locally who has it), and if that doesn't work, I will probably stop spending time on this and recreate the video material from lower quality sources I still have.


Thanks again, tsantee, for your help. If I should have any break-throughs, I will post the results here, and if you come across any other ideas, please post here as well.

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