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I'm looking for a archiving program that adds redundancy to an archive.

Example : I've got 500MB of data, and a 700MB media to burn it. Rather than waste 200MB, I want to use them to add redundancy. Then if some data is damaged, the archiving program will be able to restore it because it were redundant.

Does such a program exists ? Which one would you recommend ? If possible, a FOSS software: if you don't have the archiver source code, you don't know if you'll be able to extract the archive in the future.

Kusalananda
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color2v
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2 Answers2

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You can do it with rar. From the man page:

rr[N]  Add data  recovery  record.  Optionally, redundant information
       (recovery record) can be added to an archive.
AdminBee
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muaB
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  • Not having used `rar` myself, would the user be able to specify "give me 200 MB of redundancy"? – Kusalananda Apr 16 '20 at 11:26
  • ``rar`` is paid and proprietary software. Any FOSS alternative ? – color2v Apr 16 '20 at 12:15
  • @Kusalananda: it' percentage, but you could calculate what you need – muaB Apr 16 '20 at 12:17
  • @color2v: afaik it's not open source, but no pay-ware – muaB Apr 16 '20 at 12:18
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    @muaB: I think it's way safer to use free software for data archiving, you never know what the software will become in the future, and you can't keep the source code with the archive. – color2v Apr 16 '20 at 12:29
  • @color2v: absolutely agreed. alternatively I use snapraid (open source), but wouldn't do the job in this case anyway – muaB Apr 16 '20 at 12:36
  • If you use rar, suggest you also use its -ow switch to save file owner and group for each file archived. https://ss64.com/bash/rar.html 7z does NOT do this, else I would recomend 7z since it is open source and free. – K7AAY Apr 16 '20 at 17:14
  • @K7AAY: I can always ``tar`` before using any other tool, so it preserves permissions, owners, modes and so on. – color2v Apr 17 '20 at 11:44
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Finally, I found parchive (V1 is obsolete, use par2), which is open-source and very efficient. It was originally used on Usenet : https://en.wikipedia.org/wiki/Parchive

It has options for percentage or target size (useful on a CD/DVD/BD-R):

-r<n>  Level of redundancy (percentage)
-r<c><n>  Redundancy target size, <c>=g(iga),m(ega),k(ilo) bytes

Edit: For optical media, dvdisaster can be more relevant.

color2v
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