ISO checksums different, drive capabilities

[newbie22]

Hi,

I'm new to DVDFab but used to back up DVDs some years ago. Thought I give it another try...

So I have set up DVDFab on my desktop pc with 2 optical drives, the first an ordinary DVD drive and the second a BD drive. Copying the contents of a DVD to an iso file was easy enough. Out of curiosity I copied the same DVD to another iso file, this time using the other drive.

I would have expected to get an identical iso file and the file size actually was the same. But to my surprise the MD5 checksums of the iso files revelealed that the they are in fact different. When I compared the iso's contents file by file (again with MD5 checksums) I found that the only difference is file VTS_06_0.vob, all other files are identical.

This leads to my questions to the experts on the forum:

1. Is this expected behaviour e.g. because one of the drives is better equipped to handle copy protections? For example one drive correctly reads the data in VTS_06_0.vob while the other couldn't read some data at all and the "Full Copy" method added zero data instead?

2. If so, how can I determine which drive is better suited? Either generally or depending on the DVD to be backed up? My optical drives: "HL-DT-ST DVDRAM GHA2N" and "TSSTcorp BDDVDW SN-506BB", both were preinstalled in my desktop computer.

3. How can I check which iso file is nearer to the original? I compared both vobs with a hex editor but the parts differing were not a plain zeros so I can't make out which vob contains "good" or "better" data and which iso might contain invalid data. Is there a "validation tool" etc.? Or has DVDFab an "assessment tool" or a log file that could tell me?

Any hints greatly appreciated! Thanks!

[signals]

DVDFab writes a log file that may or may not help with this. You have not supplied enough information to really answer your questions, but you can attach the log file for these two backups to a post.

If you want to see what is going on inside a DVD, I suggest writing to a VIDEO_TS folder on your hard drive and using IfoEdit and/or PGCEdit to look at the files. Writing to an ISO introduces an unnecessary step in the process.

[newbie22]

Thanks, signals! I found the log file and it contains "1 fake vts (6) protections are removed." - guess that's why the VTS_06_0.vob is different...

So if it's a copy protection that was removed, shouldn't the result be the same when doing multiple backups of the same disk using the same drive? Creating a second iso gave me yet another VTS_06_0.vob so it seems that some random data is introduced.

On the other hand I don't really need to fully understand the copy protection and its removal...

Thanks again for pointing me in the right direction!

[signals]

You are welcome. I would have expected identical MD5s as well, perhaps it is a difference in the way the two drives firmware report errors to DVDFab, especially if the disc also has bad sector protection.