Double-layer DVDs written in data format are unreadable
Posted 11 December 2009 - 09:48 PM
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?
Posted 12 December 2009 - 12:41 PM
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.
Posted 12 December 2009 - 07:52 PM
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.
Edited by Lone Bobcat, 12 December 2009 - 07:54 PM.
Posted 13 December 2009 - 10:57 AM
Posted 14 December 2009 - 08:55 PM
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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