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My wife has a ton of data that she has worked on over the course of a decade saved on Dropbox, and we are trying to back this up to a local external drive so that we have two copies. I've downloaded all the data in chunks (from the top level folder, Dropbox complains it would be zipping too many folders), and when I try to extract some using 7zip, 7zip will complain that a handful of the files inside the zip are corrupted.

I can use the windows file explorer to go into the compressed folder and open the supposedly corrupted files (in the test case, a png file), and they open perfectly fine. It looks like exactly the file I expect.

This error is annoying because it's just a handful of files that now I have to go through and manually pull out of the zip file. Is there any way to fix 7zip so that it doesn't make this mistake? Or is there a better archive tool to use?

I can't use the windows vanilla zip utility to extract the files because that one complains that some file path names are too long (I've already changed my registry to allow long file paths, but the zip tool itself still complains about the length of the file paths).

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    Are the zip-files about 2 GB (or larger) in size? That may cause some issues although 7zip can handle them just fine normally. As @harrymc just mentioned: Just re-downloading the few problem files as a separate zip might be less hassle than trying to extract them from the largish zip-files using another tool. I wonder if WinRar (that can also extract zip-files) finds them corrupt too?
    – Tonny
    Mar 28, 2023 at 19:30
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    You should add this vital information to your question! Maybe look into rclone, it can access Dropbox.
    – Daniel B
    Mar 28, 2023 at 19:45
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    just as an aside, I do recommend avoiding using zip files (or really any other container format, but especially compressed ones) for long term archival. you are putting all your eggs in a basket and if that basket suffers a tiny bit of bitrot in the right places, ALL the eggs are gone. Mar 28, 2023 at 22:31
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    @FrankThomas If you absolutely have to use container files for archiving at least create a PAR2 recovery set (with 15% redundancy or so) for each archive file. That way you can verify and repair bitrot damage if necessary. I had a case where a client insisted on rarring old projects and burning those rars to DVD for 25 years of data-retention. After 6-7 years the first DVDs (not archival grade ones of course, too expensive) started to have some bitrot. Easily repairable with the PARs that I had the foresight to add to the DVDs. The ones made before my time without PARs had to be trashed.
    – Tonny
    Mar 28, 2023 at 23:09
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    man, par2. its been a while. I miss usenet. sucks they killed it. Mar 28, 2023 at 23:30

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