In the VIDEO_TS folder you will find several files called VTS_xx-y.VOB or VTS_xx-y.IFO. These are arranged in sets, where xx is the number of the title set, from 00 to 99.
Typically for each title set there will be a few files, eg VTS_02 may have files like
VTS_02_0.IFO 86016 84.00 KiB
VTS_02_0.VOB 258586624 246.61 MiB
VTS_02_1.VOB 1073739776 1024.00 MiB
VTS_02_2.VOB 1073739776 1024.00 MiB
VTS_02_3.VOB 1073739776 1024.00 MiB
VTS_02_4.VOB 1073739776 1024.00 MiB
VTS_02_5.VOB 866340864 826.21 MiB
The .IFO files are information files which contain information about which titles are in the set (there can be 99 titles in all on a DVD, and also 99 title sets - note, titles and title sets are not the same thing at all). A DVD may have eg 9 title sets with 27 titles spread around them.
Each title set must contain at least one title, and usually contains more than one, so there are usually more titles that title sets.
The main feature is only uniquely identified by its title, not by the title set which contains that title. A DVD player can look at all the .IFO files in all the title sets in order to find all the titles, although this information is also supposed to be in the VIDEO_TS.IFO file.
OK, when they try to stop people ripping DVDs, and sometimes for more legitimate reasons, the same .VOB files may be listed in the directory listing in several title sets, but accessed differently, eg different audio tracks etc. according to the information in the .IFO file for that set.
This means that the same 1.1GB .VOBs may appear several times in the directory listing with different VTS numbers - they are a bit like links to files rather than files themselves.
Not being very clever, many programs try to reproduce the directory listing - and rip the same set of 1.1GB files several times. This leads to very large, like 64GB, VIDEO_TS folder rips even though the DVD itself only holds about 8 GB.
For dvdbackup the best way to avoid this is to tell it the title you want to rip, eg
dvdbackup --title=24 --start=1 --end=17
where 1 and 17 are the first and last chapters of the movie, and 24 is the title which is played as the main feature. You don't actually need to include the start and end numbers, but it helps.
If you can play the DVD in eg movie player, zine or VLC they will tell you the right numbers to use - the title number appears in the window title bar when the main feature is being played, the chapter numbers can be found easily enough in the usual places.
Incidentally this is why you get the same errors at the same places - it is reading the same lots of data ("files") several times.
Sometimes as an anti-ripping measure they put deliberate errors in, and the correct "link" is made to somewhere after the errors, not to the beginning of the data - so only the correct "link" will work, and if you try to play the files from the wrong link they won't play. Alternatively the deliberate error is in a place which doesn't get used in normal play for that title, eg if the german audio isn't being used.
This can get very complex, but the resulting DVD has to play on DVD players - which limits what they can do.