7-Zip very slow?

Help
2004-12-21
2012-12-07
  • I have a directory with roughly 16.000 files, 1.000 directories, that uses 1 GByte. I want to archive it so that I can delete the original files and save space on the hard disk. I had the idea to use it to compare different software. For each software, I tried to set the best compression. 7-Zip seems to be able to create the smallest file, but it is very slow if compared with ace and rar. I used these settings:
    Archive format: 7z
    Compression level: Ultra
    Compression method: LZMA
    Dictionary size: 16 MB
    Word size: 255
    Solid archive: Yes
    I did not specify any additional parameter
    My computer has a 2.80 GHz Pentium IV and 504 MBytes of ram.
    What are the settings that I should choose to get the best compression and still work in a fast way? I understand that I cannot get everything, but it is possible that with some settings I get 99% of maximum compression, and I can use the true maximum compression if I accept to work in a slow way. If this is the case, I would agree to get "only" 99%.

    Thank You very much

    Rodolfo Giovanninetti

     
    • Ares
      Ares
      2004-12-22

      Well, for starters you *might* want to add a little extra RAM.  Once Windows starts swapping out 7-zip, things get ugly.  Try closing as many background processes as possible first and see if that helps.  If so then you'll probably want a little extra RAM.  Also try using a smaller word size (64 or so).  Unless there's a lot of text files in there with similiar phrases, a word size of 255 is only going to save you a few hundred KB.  The word size alone can make a huge difference in speed.  I would try Ultra at 64 word size, and Max at 64 word size - with as many programs closed as possible.  That's just my guess.

      I too have a P4 2.8Ghz w/512MB of RAM.  Ultra works very very slowly at 255 word size, but is much quicker at 64 word size.  Also, if your disk starts churning a great deal and you drop below 150kb/sec, and start going into double-digits, chances are Windows is swapping out 7-zip.  That's where all the speed goes.

      Also, the files you are compressing can greatly increase the time.  Especially if they are already compressed.  This can drive 7-zip crazy (aka make 7-zip go very slow) if you're using the max word size and trying to compress not-very-compressionable data.

      Just my 2 cents worth - I'm by no means an expert, just a daily user of 7-zip with similiar system configurations ;)

      So try closing everything out first, if not use a smaller word size (around 64), then take it down a notch to Max if need be.  That's what I'd try.  Good luck!

      Ps. I've never really seen speeds past 600kb/sec and that's with the Fast setting.  I've never seen Ultra go much over 350kb/sec either.  It usually goes about 125-175kb/sec for me.

      -Ares