7z archive been fine for years but suddenly CRC error

[RageTester]

Quote

Corruption case: Data errors or CRC errors for files inside archive

Here we describe the case, when you can open archive and you see the list of files, but when you press Extract or Test command, there are some errors: Data Error or CRC Error.

It's pretty difficult to recover data for that case.

If archive was compressed in "Solid" mode, and you have exact copies of some files from archive, you can create similar archive with good copies of files with same settings and in same order, and replace "bad" parts of bad.7z with "good" parts from another good.7z. You must look listings of files in bad and good archives, logs of "test" command, and think about ways to replace bad parts.

The are no more instructions here for that corruption case.

What might have caused files inside archive to go bad? I copied them from one hard drive to a newer one and now I can't view half of the images. I don't recall and error during transfer and this makes me rethink storing any files inside archives...

And more different errors...

 

[Kilrah]

If the source drive had a failing sector or something it could have led to a copy error - and on an archive the entire archive goes bad.

Not a great idea to store valuable stuff in archives.

[Wiebenor]

You can easily store stuff in archives, but due to that exact problem, if it's an important archive, that you have to have, then I would save both the new and old copy, and if the new copy doesn't extract properly, then I would try to extract those missing files from the old copy of the archive, and if that works, then it was a copying issue... now for a bit of advice for archive users in general... If it's a game, or other application, I would suggest redownloading the torrent, or other file, or else, better yet, just buying the game or other software, assuming that it isn't free to begin with...  Also, if it's that important, I'd make a backup every time you build large 7z files

[Master Disaster]

If you insist on storing files in archives then look into pararchives. They allow you to create parity files from any file on your computer and if the file ever becomes corrupt recover them back to the last working version. The catch is every time you add a file to an archive you need to remove the par files and recreate them.

 

http://www.quickpar.org.uk/

[Wiebenor]

10 hours ago, Master Disaster said:

If you insist on storing files in archives then look into pararchives. They allow you to create parity files from any file on your computer and if the file ever becomes corrupt recover them back to the last working version. The catch is every time you add a file to an archive you need to remove the par files and recreate them.

 

http://www.quickpar.org.uk/

Sounds a bit like WinRAR... They have an option to dedicate a certain amount of space to what amounts to a recovery volume, although when I can get seven zip for free I would never use winrar except for the executable creation myself but it is an option... And I haven't actually heard of your option specifically but it sounds like it should work as good or better than the WinRAR option... Although, that won't fix the guy's current situation assuming that this is more than just a scenario and something that actually happened...