Help on archive corruption

  • Davide

    Davide - 2014-01-14

    Hello, i explain my issue.
    I store my data in several .7z files (most of them made manually, someone made via Cobian Backup 11).
    Now i have found an archive (a .7z file with about 1200 images, 2 Gb) with about 12 images corrupted; the error message says that password (just numbers and letters) is invalid for 12 files but is the same for all archive, i'm sure because i have opened it about 6 months ago without any issue.

    2 question:
    1) how can this happen ? my hard disk is new and in perfect condition
    2) how to avoid this issue ? i need a newer version of 7-zip ?

    Actually i use 7-zip 9.20 (latest full non beta/alpha version), 64 bit, on Win 7 Pro 64 bit.
    Hope you can help me, thx :)

  • Igor Pavlov

    Igor Pavlov - 2014-01-14

    If you updated archive, it's possible to add files with another password.
    If you didn't update archive, than probably it can be some hardware error (HDD error or RAM error) during creation / storing / transferring or extracting.

  • Davide

    Davide - 2014-01-14

    Thx for reply. No, i'm sure. archive has never been updated. I've created it 2 years ago and I full extract it every (about) 5-6 months. No issue with this rchive until yersteday.

    So, is not possibile is an hardware error during creation (because i've already full extracted the files) and, of course, i've tried extraction on different computers.
    My hard disk is a SSD, 1 years old, perfect condition and cloned weekly.
    If the file has been corrupted due to a hd error i think that I should have noticed some other error or some SMART report, or not ?

    Can be some kind of 'bug' of 7-zip 9.20 version ? Maybe with the newest SSD ?
    Are reliable the .7z archives ? Sorry if I ask but now i have about 10 archives and i'm scared to discovere more corrupted file inside the .7z :((

    • Shell

      Shell - 2014-01-15

      I don't believe it is a 7-Zip's bug. Have you checked SMART data? The overall status may be "good" even for faulty disks. For example, my HDD has 14 reallocated sectors - this means their original contents has been lost once - but I have received no report on that. Check the relevant attributes (5, 187, 197, 198), and check the archive's data with a hex editor (reallocated sectors are usually filled with zeros).

      Maybe the SATA cable is overbent or poorly attached - this usually causes CRC errors during transfer which are logged in SMART (attributes 195, 199). Most of them may be corrected by the hardware, but some can lead to data corruption. If this happens during creation of an archive, it will be permanently damaged; if this happens during read, then you will see a transient error which may or may not reappear. I suggest you to test the archives after creation and, as Igor Pavlov suggests, to check the important data against its mirrored copy.

      P.S. .7z archive format is, perhaps, less reliable than several commercial formats because it lacks recovery data. However, no archive is completely error-proof, so it is advisable to back up the important data regularly, just as you do when you clone your disk.

      Last edit: Shell 2014-01-15
  • Igor Pavlov

    Igor Pavlov - 2014-01-14

    Check also RAM

    If you have the copy of archive, you can try to make byte to byte comparison.

    With latest 7-Zip 9.32 you can calculate checksums:
    7z t .7z -scrc > test.txt
    7z h
    .7z > crc.txt
    Then store these 2 files.
    If you think that something is corrupted, can it again and compare crc values in crc.txt.

    In general, I think that ssd/flash is not safe technology still to store data.

    Last edit: Igor Pavlov 2014-01-14

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