Can burning an additional session ruin a multisession DVD completely?

This is a question for those who know the format of a multisession DVD:
I burnt a multisession DVD with several sessions. I checked the contents after each session, all was fine.
Now while burning an additional session the computer crashed.
The result is that  I can not read any session from this DVD any more.
As the average naive user I assumed that all the sessions already burnt on a DVD should be safe, even if something happens in a later session.

So my question is:
Was this an extremely unlikely incident, or is it quite normal that one session which is messed up ruins the previous sessions as well? And why is that this way or the other?
JustAHintAsked:
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rindiCommented:
The crash would cause this as has been mentioned, not burning the extra session. You should be able to recover data on that DVD with isobuster.

http://www.isobuster.com/

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kgreeneitCommented:
it seems like the system crash has corrputed your DVD's contents and as a result messed up the pointers from all the other sessions. You could try and 'close' the disk using your DVD burning software and see if this re-enables the previous sessions. If not, then there's probably nothing you can do. Generally you wouldn't need to close a disk until it is full or you are happy that you dont want any more sessions on it, but in this case closing may retrieve what you're looking for.
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JustAHintAuthor Commented:
I just want to know how the contents of the multisession DVD is organized. I.e. since it is just a DVD+R it should not be possible to alter data which are already written in previous sessions. Or is it possible that an area on the DVD which is already used for data of a previous session is "overwritten" i.e. messed up later? Or is this prevented by the hardware?
Or is there no standard way to write a multisession DVD and each burner, each burning SW, each operating system does that in a differen way so nobody knows what could happen?

I want to get a feeling how safe it is to use a DVD for daily incremental backup. If there is a more than marginal possibility that I burn some days without problems and then the next session ruins the disk completely, then I can not use it for that purpose.

The operating system used is Windows 2000.
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kgreeneitCommented:
hi there, I wouldn't be too comfortable with using DVD+R 's to backup up data on a regular basis. DVD+RW's would be a better choice as they usually handle multiple session's a lot better. I wouldn't generally recommend using a DVD to backup data as there is never a guarantee that the session will complete without errors. Anti Virus software for one can cause nightmare's when buring DVD's or CD's and if you are backing up data on a server, then you should really try and get something like a HP Dat drive or similar to do the job. The capacity would be 10 times the capacity of a standard DVD too.
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rindiCommented:
No, never get dat, that is just about the most unreliable tape system there is. DVD-R's aren't that bad. Just regularly restore your data for testing purposes, and open the restored files with the original apps. That's the only safe way to make sure your backups are OK, and this is a must with any backup and any backup media. Also, a crash can also cause other media to get corrupted enough for the data to be difficult to be recovered later, whether that is a tape, CD, DVD or HD.
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JustAHintAuthor Commented:
I will try your suggestion to use isobuster tomorrow. Thanx for the hint.
Up to now I thought tapes to be unreliable. On more than one occassion when I tried to retrieve data from a tape after some months the tape was corrupt.
The capacity is not an issue here since a month of data fits on a DVD easily.
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rindiCommented:
Dat, and very often also travan aren't reliable. Most other tapes I know of aren't a big problem. It is important that a tape shouldn't be used to many times, whereas disks are more for constant use. If the tapes are stored in cool, dry places they should last long. Also, if the tape was good after the backup (hence the restore test) and stored properly, it shouldn't corrupt after a few months.
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JustAHintAuthor Commented:
As I understand now:
When a multisession DVD is written, the new data is not appended to the catalogue, but the old catalogue and the new files are written to a new catalogue. I.e. if this new catalogue has been corrupted the full contents of the DVD is no longer accessible. With Isobuster it is possible to access the previous catalogues which may enable to retrieve the data from the previous sessions.
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rindiCommented:
I don't think isobuster is even absolutely dependent on catalogs. If it finds none or can't read them, it just tries to read the data.
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