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I frequently need to do a backup of a group of files, with many subfolders which contain several large, identical files.

Is there a compression scheme (.zip, .7z, etc) which can automatically detect this and not store identical files more than once?

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which operating system are you using? –  Daniel t. Mar 1 '13 at 0:01
    
I'm on Windows (7) but the files are on a network, so I could run the compression app on any OS. –  Warpin Mar 1 '13 at 0:30
    
you can google for incremental backup. –  Mohsen Pahlevanzadeh Mar 1 '13 at 0:43
    
incremental backup doesn't seem to help, as new files (many identical to existing files) are created in new folders. –  Warpin Mar 1 '13 at 1:32

1 Answer 1

up vote 0 down vote accepted

Yes, it's possible: http://superuser.com/questions/479074/why-doesnt-gzip-compression-eliminate-duplicate-chunks-of-data

Here's an example I came up with:

[jay test]$ tree .
.
`-- compressme
    |-- a
    |   `-- largefile (10MB)
    `-- b
        `-- largefile (10MB, identical to ../a/largefile)

3 directories, 2 files
[jay test]$ du -sh compressme/
21M compressme/
[jay test]$ tar -cf compressme.tar compressme/
[jay test]$ du -sh compressme.tar 
21M compressme.tar
[jay test]$ lzma -9 compressme.tar
[jay test]$ du -sh compressme.tar.lzma 
11M compressme.tar.lzma
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