Problem with extracting compressed and splitted data

  • zerotips

    zerotips - 2013-12-18

    I have a huge problem. I had some files on my laptop and I wanted to put them all on DVDs before OS reinstallation so I have used 7zip to compress and split them into 4 parts of the size of DVD. After that I have used Free Easy Burner to burn those parts on 4 DVDs and I did OS reinstall. After that I have tried to copy files from DVDs back to PC and ran into a problem. DVD was full but zipped and splitted files were only ~400 MB big, each of them. I have tried to merge them and unzip with 7zip but it returned "Unknown Error". I have tried to use other programs similar to 7zip, but none worked.

    After that I have created images of the DVDs and saved them on laptop by using Free Easy Burner. Each image file had size of a DVD, ~4.4 GB, but when I open .iso file I can see only ~400 MB file in each of .iso files. I have tried to unpack .iso files with a few programs but all of them extracted ~400 MB files from ~4.4 GB images.

    I don't know if it matters, but I have made 7zip archives while I was using Windows 8 and now I use Windows 7 while I am trying to extract them. Also, if I remember correctly, I have used default settings for compression. One more thing, during extraction of the 7zip files from .iso files, it shows level of compression of around 1000% which may have some connection with the proportion of the 4.4 GB size of the .iso and 400 MB size of the 7zip file.

    So, now I have a huge problem because among the compressed files I have many important files that I need to access and I am unable to do it. Anyone who can help me will be my hero for the rest of my life.

    Here is the picture that sums up my current situation if I was not clear enough because of my not-so-extraordinary English...


  • Igor Pavlov

    Igor Pavlov - 2013-12-18

    Install 7-Zip 9.32 alpha.
    1) try to open iso with 7-Zip 9.32.
    if it doesn't help, try another way:
    2) insert dvd disk
    run 7-Zip 9.32 with admin rights
    go to root folder in 7-Zip file manager


    and try to open your disk.

    if it doesn't help
    Extract 400 MB 7z.001 (look first bytes in hex editor).
    Try to find same bytes in .iso
    detect start address
    Split iso into 3 parts with 7-Zip (you can write list of sizes with spaces between size):
    1) Head (everything before start of 7z.001 )
    2) 4 GB + (exact size of 7z.001 that you see) (probably it's real original size)
    3) some tail data

    maybe the part-2 will be OK file.

    And do same things with another 4 iso files.

    Last edit: Igor Pavlov 2013-12-18
  • zerotips

    zerotips - 2013-12-18

    Thank you a lot! I will try it and report the outcome.

  • zerotips

    zerotips - 2013-12-19

    Ok here is the update on the problem. I have tried first two things and it didn't work. Same thing happened as before. For the third thing, there might be some progress. I have opened .iso file with hex editor (HxD). It consisted of three parts:

    1) bunch of 00 blocks;
    2) part with data that starts with same hex values as extracted 7zip archive;
    3) again bunch of 00 blocks.

    Now, the part 2) has size of exactly 4480 MB (4697620480 bytes) which is the exact size that 7zip splits archive into when DVD size is selected, which I have used in the first place. My guess is that the part two is the real 7zip archive and that somehow upon extracting it detects end of archive on the wrong place.

    Here is what happened when I tried to merge splited archives of the size ~400 MB.


    Also, after I have splitted the .iso file with 7zip into 3 files, one of which had size of 4480 MB and was supposed to contain the middle part of .iso file (part 2) from the above), 7zip said that it can't open that file of 4480 MB as archive. I guess the problem is because it is kind of archive in archive...

    So, what do you suggest me to do now? I see the only option in manual copy/paste the part 2) of the .iso file into a new file and then trying to open it with 7zip. With a lot of luck I think it might solve the problem. Also, do you know some faster way of extracting part 2) from .iso since it doesn't allow me to copy to clipboard more than 500 MB of data and I have much more to copy than that so it would be some pretty slow process.

    Last edit: zerotips 2013-12-19
  • Igor Pavlov

    Igor Pavlov - 2013-12-19

    You must do same for all iso files from these 4 DVDs.
    Then place these 4 files to one folder:
    Then you can try to open .7z.001 with 7-Zip.


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