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Is PAR2 recovery system good for all of us?

2005-02-22
2012-12-08
  • I tried PAR2 utility (suggested by Igor), and I think it's very good to repair large files or sets downloading a few recovery blocks only from the Internet...
    But it seems that it's not so good in the environment where I mostly need recovery capabilities: the floppy disk.
    In fact, recovery method first introduced in RAR archives is fast and cheap: it takes a CRC-16 for each 512 byte file sector and 1 or more recovery sectors made XORing all sectors belonging to different input blocks at the same distance.
    So, protecting a 1410K file on a floppy requires about 40K and permits to restore 32K of data: on the contrary, obtaining the same result with PAR2 is impossible, since it emits too large recovery files selecting a so small sector; while switching to a larger sector makes recovery less careful -a floppy disk tipically corrupts a few contiguous sectors in 1 or 2 positions.

    So, what is (are?) the best technique 7-zip should introduce?

     
    • WinRAR superiority once again!!!

       
    • Stepho
      Stepho
      2005-02-22

      You again ?!
      May be one day you will understand that WinRAR is a commercial product and 7-Zip is a free (open source) project. Igor Pavlov cannot work on 7-Zip fulltime.

      You cannot complain about something you didn't pay for, or something nobody forces you to use. The author allows us to benefit from his work, and for that you should be grateful.
      If you're not happy, begone ! and good riddance !

      Of course, I know you just want a little attention, that's why you keep hanging around... cause you probably don't have anything better to do, child...

       
      • Igor Pavlov
        Igor Pavlov
        2005-02-22

        > Igor Pavlov cannot work on 7-Zip fulltime.

        I work fulltime for 7-Zip and LZMA SDK. But most time it's thinking :)
        For example, two last weeks I tried to increase speed of LZMA compressing. But 90% of ideas doesn't work. Maybe there will be only 2% of speed improvement in next versions.

         
    • Where am I complaining? Just stating the facts!

      Child...

       
    • Stepho
      Stepho
      2005-02-22

      I am assuming that you are the same who posted in this thread about multi part RAR archives (http://sourceforge.net/forum/forum.php?thread_id=1229479&forum_id=45798).

      If you are, you are complaining; if you're not the same person, you look the same kind of person, but in doubt, I may owe you some apologies. In any case, you should register a sourceforge account to avoid anymore confusion.

      Everyone here knows 7-Zip lacks some important/useful features (multimedia filters, date recovery, GUI improvements, ...). These features are either under developement, either planned or not. If you use 7-Zip you can only accept it.

       
    • Stepho
      Stepho
      2005-02-22

      > > Igor Pavlov cannot work on 7-Zip fulltime. 
      I won't say it again :-)

      I'm not very knowledgeable about compression algorithm (I only know run-length encoding, and Huffman codes). But I know about rethinking complex algorithm and applications, so i understand the "thinking" :-)

       
    • "I work fulltime for 7-Zip and LZMA SDK." woops.
      How many hours a day? (just curiosity)

       
    • I didn't mail any previous message, I don't say WinRAR is superior (on the contrary!!!)...

      I only wanted to start a discussion about future 7-zip improvements... A suggestion isn't a crime, I hope!!!

       
    • Stepho
      Stepho
      2005-02-23

      > I didn't mail any previous message, I don't say WinRAR is superior (on the contrary!!!)...

      > I only wanted to start a discussion about future 7-zip improvements... A suggestion isn't a crime, I hope!!!

      If you are the original poster, my angry answer was for
      > WinRAR superiority once again!!!

      It's not my place to say, but I think suggestions are welcome. Have I know anything about data recovery, I would have happily taken part in the discussion you have started. :-)

       
    • I love that when the talkling heads heat up over important matters dear to their heart. :))
      2% speed improvement is better than zero!

      -R (dt)

       
    • PAR2 IS the right way to go, just because you can add as much redundancy as you want. If you have a 20 CDR multivolume archive, you can add 1 GB redundancy, loose one CDR and will still be able to recover all the data.

      I did the following for testing:
      *made a multivolume 7z archive - vol. size 650 MB
      *16 volumes were needed
      *calculated 16 par2 files with 7.7% redundancy
        - 50 MB each
      *copied n'th volume from the multivolume set with n'th par2 file to one CDR

      result:
      I can now restore one completely lost CDR AND some CRC errors additionaly.

      Integrated and configurable PAR2 would be a GREAT Feature for 7zip !