Corrupt DVDs

ddrescue, but don't hold your breath

ddrescue is the standard one. Also try dvdisaster (its mainn purpose is to add error correction, but it does repeated reads too).

Reed Solomon corrects errors up to 10**4 on the error scan.

Above that level, usually the laser is no longer able to track the groove. The groove tracking method is different on "+" and "-" media, and one of those is better than the other. Not that this matters with some pressed media you can no longer read.

A sign the laser is not locked, is the computer DVD drive "loses its mind". The processor is kinda busy slapping the arm around, looking for the groove, and it stops listening for the button press on the front of the drive. You can have difficulty getting the tray open, if the laser cannot lock. In some cases, shut down the OS, and use an unfolded paper clip to shove into the release hole (to make the tray open a tiny bit).

DVD media uses a spiral groove. DVD RAM media uses a series of concentric circles instead, and DVD RAM functions similar to how a hard drive works. But for regular media (anything not DVD RAM), the groove is spiral, and the edges of the groove contain an encoding the laser picks up at read-power-level. The laser is programmable, so the power level is not fixed. It has read, write, erase power levels. Write and Erase don't work on pressed media (such media being Read-only). The "media tag" on a media, contains info about what power levels this particular media might like. Drives work best, if they "recognize" the media being inserted.

But once the chemistry is fouled up beyond repair, the laser is not going to lock. If it can't track the spiral it cannot read the data contained in the spiral.

Many thanks for t he replies :-)

I have found a used set of the damaged season for £4.02 inc postage so I've ordered it, if it works it will be less frustrating than trying to scrape the data.

I have an HP ProLiant MicroServer Gen8 coming from eBay this week, it will be used as a home media server running Linux Mint Mate. Once it's here I'll set the old machine running ddrescue on the DVD if only to see how it works and how effective it is.

Thanks again!

I think your £4 purchase is a sounds move. That's maybe a pint of cheap beer. However, can I suggest you use the duff DVDs and play with ddrescue et al. and see if you can actually recover the data. One day there may be no cheap options and you'll know what actually works etc.

GNU ddrescue is the best recovery software that I have used. It is much better than any of the commercial programs that I tried when I really wanted to recover some data. The advantages include: If it has trouble reading one area it then starts again from the other end of the media so that it can grab as much good data as possible before it wears out the drive. It remembers what it has already recovered in a log file so it doesn't need to start from the beginning again if the system crashes - which is quite common when reading damaged media.

Most important of all, as I discovered the hard way, DO NOT USE WINDOWS for data recovery. If a hard drive starts out unreadable to Windows and the recovery software creates a new version on another drive that can be understood by windows and Windows crashes, after rebooting it will then try to fix the recovered drive. This makes it useless for ongoing recovery because Windows has moved things around.

John

There is actually a product made by a small developer, that is better than gddrescue package. How it is better, is it uses a custom hard drive driver file, and the retry interval is truncated. That means the utility is a custom only for HDD usage. Not for ODD or SSD.

In a test I did, the utility was able to read a hard drive that had ~100 unrecoverable errors. It did that, in approximately a day. Whereas when I tried to use ddrescue, it promised that the scan would take thirty days to complete (because the drive would be spending 15 seconds trying to recover a single sector). ddrescue would have achieved a better read rate, once it got through the rubbish at the beginning of that disk.

This is a picture showing how much each utility could recover in a 24 hour day. The HDDSuperClone in that example, is "finished", and then a user could figure out from the list of bad addresses, whether white space was damaged or files were damaged.

Paul

I see lots of discussion of recovery tools in this thread, but no info in answer to the first question.

See

Many thanks Geoff :-)

I waited to reply until my £4 used set arrived. I go it yesterday and it is absolutely fine so I will ditch the original and keep the replacement.

Good to know what the problem is, hope it's not infectious!

I used to buy a lot of used DVDs from CeX... ~1 in 50 didn't work, Sometimes they polished up, sometimes they did not.