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Problem recovering data from DVDR

 
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rimara



Joined: 30 Jan 2006
Posts: 5

PostPosted: Mon Jan 30, 2006 1:55 am    Post subject: Problem recovering data from DVDR Reply with quote

Here is the problem:

1. I stored several video files on DVD
2. I created an .ecc file and verified the data and the .ecc file - all ok. I also verified the .ecc file by testing the data on the HDD before deleting.
3. Later, when I try to copy the files from DVD to HDD, I get a cyclic redundancy error, something is wrong with one of the files.
4. I believe the file is marginally written to the DVD. It is a video file, and sometimes the video application plays it fine, somethimes it locks up.
5. When I verify the DVD through ICE ECC, it says the data is OK and therefore will not recover the file!

The problem is that ICE ECC can read the file but Windows can't. There is no doubt that ICE ECC could have recovered the data, but since it thinks it is good, it will not. This could be the case with any file that that has degraded and become hard to read on a DVD.

I was able to eventually recover the data by copying everything but the 1 bad file to the HDD and recovering the 1 missing file with ICE ECC. I was lucky because the bad file happened to be smaller than the ECC file. If the bad file had been larger, I would have lost my data. My last resort would have been to try and mark the DVD so that ICE ECC thought the file was bad.

Is there a way to FORCE a recovery of data? I believe this functionality is needed. I am certainly not willing to take a chance with ICE ECC now that I have had this bad experience.

Is there another way to handle this problem that I am overlooking?

rimara.
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rimara



Joined: 30 Jan 2006
Posts: 5

PostPosted: Mon Jan 30, 2006 2:55 am    Post subject: Reply with quote

After further experimentation, I continued to let ICE ECC verify the files on the DVD. The first time it verified the data as good. The second time it found a bad block (Damaged block - 3555) and then started recovering the data and then failed. Here is info from the log:

*********************************************

File read error - D:\movies\western.wmv
Damaged block - 3555
Verify ECC Files
Some files are damaged. Recover is possible
Matrix calculation - 0
Recovery Data Files
File read error - D:\movies\western.wmv
Block read error - 3556, B
Recover failed
Verify failed

*********************************************

What this means to me is that the DVD is hard to read and sometimes a block can be read and sometimes not. ICE ECC knew block 3555 was damaged, but was not expecting 3556 to be bad and failed the recovery. This means that ICE ECC will not recover your data if during recovery it encounters a read error in a different block than it did during the verification process.

I will continue to experiment to see if ICE ECC will recover the data.

rimara.
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rimara



Joined: 30 Jan 2006
Posts: 5

PostPosted: Mon Jan 30, 2006 4:34 am    Post subject: Reply with quote

More experimenting/testing....

Here is my latest failed attempt at recovering data from a bad DVD:

******************************************
ICE ECC v2.2.1
Physical Memory - 1023 MB
Memory Usage - 614 MB

Speed - 550.05 MB/Sec
Configuration - 1, 0, 4

Verify Data Files
File read error - D:\movies\western.wmv
Damaged block - 3555
File read error - D:\movies\western.wmv
Damaged block - 3559
Verify ECC Files
Some files are damaged. Recover is possible
Matrix calculation - 0
Recovery Data Files
File read error - D:\movies\western.wmv
Block read error - 3553, B
Recover failed
Verify failed

******************************************

It looks like ICE ECC is failing the recovery because there are several blocks that cannot be read reliably. I have over 200 blocks of ecc but still cannot recover the few bad blocks. In this case, during the verify stage, ICE ECC thought that blocks 3555 and 3559 were bad. It determined that it could recover this, but during recovery, it had problems reading block 3553 and recovery failed. This is similar to the previous test.

The way it stands right now, I don't think anyone can rely on ICE ECC to recover a degenerating DVD in the future. If there are several blocks that the optical drive is having problems with, it would be expected that those blocks may read differently at different times. If the disk reads differently during the verify stage than the recovery stage, your data is not recoverable! This is even the case when you have more recovery blocks than bad blocks.

I do not know what it would take to correct the code but ICE ECC needs to be able to repair DVD disks that do not have repeatable reads. Maybe if ICE ECC would restart the recovery process if it encountered additional bad blocks and add those blocks to the bad block list. Additionally, I still think that ICE ECC needs to be able to be made to recover the DVD disk even if no errors are found during the initial verification.

rimara.
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Glyph



Joined: 05 Jun 2005
Posts: 31

PostPosted: Tue Jan 31, 2006 10:22 am    Post subject: Reply with quote

Try using a DVD recovery program like ISOBuster to read all the data off the DVD first including the bad blocks onto the hard drive.

then use ICE ECC on the files on the hard drive.

ISOBuster will copy files even if they are damaged, it won't stop and ignore them like windows does.

I once had a very badly damaged DVD where every single file had a large number of errors, Windows wouldn't copy a single one. But ISOBuster copied them all and then i was able to use ICC ECC to fix them.
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rimara



Joined: 30 Jan 2006
Posts: 5

PostPosted: Tue Jan 31, 2006 7:38 pm    Post subject: Reply with quote

Thanks Glyph,

I ran Isobuster on that one file and tried to extract it to the HDD. It said it found bad blocks or clusters or something so I told it to ignor that. After many hours, I found that the file had been copied but with errors and was smaller by about 10 MB. When I ran ICE ECC on the HDD archive, it found errors in every block of the copied over file. It should have found some usable blocks, but apparently the damage affected every block. Unfortunately I still do not have a reliable solution.

Since recovering data from a deteriorating DVD is different than recovering data from a HDD, I believe that ICE ECC needs to be able to adjust for inconsistent read results. I believe that ICE ECC would be a much more robust DVD data recovery tool if it would do the following:

1. Verify button. Change to "Verify and Recover". ICE ECC recovers data to indictated directory even if no errors are detected during verify. If no recovery is desired, then use "Verify Only" button. This is useful in the case where ICE ECC finds no error, but Windows has read errors and will not copy files from DVD.

2. Handle new read errors during the recovery process. ICE ECC updates the bad block list and restarts the recovery process. I expect that this restart process would be somewhat rare and would not affect performance in most cases.

At this point, I am not so worried about processing time but am worried about getting my data back. Absent the above changes, I have been thinking about ways to get around these problems. I was thinking of taking my archive files and converting them to multiple RAR archives and then creating an ICE ECC of those files. In the event there were read problems with the DVD, I would remove as many of the RAR archives as I could to the DVD and then perform the recovery there. If I was going to do that though, I might as well use the built in ECC function in WinRar.

With that thought in mind, what are the downsides of using WinRar's ECC functionality? Thoughts?

rimara.
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rimara



Joined: 30 Jan 2006
Posts: 5

PostPosted: Thu Feb 02, 2006 5:44 am    Post subject: Reply with quote

Success!!! I went back to Isobuster and did some more reading. What I did was to extract the entire image file (tao) to the HDD. When Isobuster encountered the first bad block, it asked me if I wanted to do either of the following:

1. Omit data
2. Replace with all zeros
3. Replace with dummy data

I selected "Replace with all zeros". Once the image file was on the HDD, I opened the tao file with Isobuster and extracted all of the files to the HDD. I noticed immediately that the file size of the one bad file now was correct. When I had done the extraction before with Isobuster, I had just extracted the file alone and the resulting file was considerably smaller. I suspect that the file structure had been damaged during this "single file extraction". When I had extracted the whole image, the correct structure appears to have stayed intact for the bad file.

I then ran a verify using ICE ECC and found that there were 4 bad blocks and then completed the recovery.

Thanks again Glyph for pointing me in the right direction, I think I have a workable solution now. I would still like to see modifications to ICE ECC that would make these extra steps unnecessary.

rimara.
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