Corrupt .zip archive

Discussion in 'Computer Information' started by NGs, Sep 1, 2012.

  1. NGs

    NGs Guest

    I all, I'd like some advice on the following:

    Today I downloaded an .iso file in size and all neatly wrapped up in a .zip file in excess of 4.5 GB all up.

    When I went to unzip the .zip file it worked for a nanosecond then a message came up telling me the archive was corrupt as per

    "! C:\My Documents\Cool The archive is corrupt"

    My question is; is there any way I can pull useable files from this mess? If so, how would I go about doing just that?

    Would anyone know of a way to repair the archive?

    TIA for any and all assistance.

    NGs, Sep 1, 2012
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  2. NGs

    Paul Guest

    That depends to an extent, how much the information at the beginning or
    the end, of each level of container, plays a part in its recovery.

    If the directory information was at the front of both ZIP and ISO, then
    you'd think that recovery of the available percentage would be possible.
    If ZIP has a critical parameter, written at the end of the archive,
    then you could be screwed.

    As for what happened in the first place, my guess is you downloaded
    to a FAT32 partition with a 4GB maximum file size, and the 4.5GB download
    stopped at the 3.999GB mark. That could be the nature of the corruption.

    Tools like 7-ZIP, have a habit of doing "random access" on archive files,
    checking whatever they feel like. So a tool like 7-ZIP, the GUI version,
    might stop before it even got started.

    If I was trying to recover the thing, I'd use a command line utility, one
    with "pipe" capability, so it was forced to only deal with the archive
    file sequentially.

    If it was gzip, it would be something like

    gzip -c -d corrupted.iso.gz > corrupted.iso

    Maybe there is a winzip utility of a similar nature ?

    unzip -c corrupted.iso.gz > corrupted.iso

    Next, you pop the corrupted.iso into an ISO9660 recovery tool (normally
    used for optical disc recovery). I suspect the directory is near the front,
    so only the data clusters got chopped off. And the files at the end will
    go missing.

    I don't know enough about the formats, to tell you what your odds
    are of getting anything. For all I know, it could be a wasted effort.


    At one time, at least some web browsers, could "restart" a download, at the
    point it was stopped. But, to do that, none of the initial conditions could
    be changed. If you tried to move the file (like, move the damaged file
    to a different NTFS based partition), the download code would insist
    on starting the transfer from zero. Since one possibility, is your partition
    was FAT32, it would be difficult to trick the browser into picking up
    where it left off. While Windows has the "convert" utility, to change
    a partition from FAT32 (4GB limit) to NTFS (no practical limit), what
    are the odds that would fool a browser into doing the right thing ?
    By changing partition types, you take the 4GB cap off, and if the
    transfer was restart-able, another 500MB of download and you'd be finished.

    convert e: /fs:ntfs /v

    But that's a long shot. And could mess up something else you're doing.

    When I made that mistake (download >4GB file to FAT32), I just
    started the whole damn transfer over again. And as far as I can recollect,
    I haven't made the same mistake a second time. I always check now, before
    I start the transfer (I guess the first mistake was a "Doh!" moment
    for me :) As soon as you see the thing bomb out, you know right away
    what happened... ).

    (Paul learns about FAT32...)

    Paul, Sep 1, 2012
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  3. NGs

    NGs Guest

    I was downloaded to a NTFS partiton, but anyway, I managed to repair the file using something I found after I did a search for zip
    file repairs, and was able to extract all the data from both the zip and the iso

    So thank you to the replier for taking the time to relay the information to me.

    NGs, Sep 2, 2012
  4. NGs

    Paul Guest

    So it was just a bad download then (full sized, but bad checksum) ?

    Good repair work.

    Paul, Sep 3, 2012
  5. NGs

    markmvps Guest


    Kernel for ZIP recovers multiple files from corrupted ZIP archives corrupted due to incomplete download, virus attacks or CRC errors. During repairingprocess a complete scan of the damaged ZIP file is performed to locate andextract the recoverable information.You can get a free demo from here
    markmvps, Feb 13, 2013
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