Aug 22, 2015

Quick lzma2 compression showcase

On cue from irc, recently ran this experiment:

% a=(); for n in {1..100}; do f=ls_$n; cp /usr/bin/ls $f; echo $n >> $f; a+=( $f ); done
% 7z a test.7z "${a[@]}" >/dev/null
% tar -cf test.tar "${a[@]}"
% gzip < test.tar > test.tar.gz
% xz < test.tar > test.tar.xz
% rm -f "${a[@]}"

% ls -lahS test.*
-rw-r--r-- 1 fraggod fraggod  12M Aug 22 19:03 test.tar
-rw-r--r-- 1 fraggod fraggod 5.1M Aug 22 19:03 test.tar.gz
-rw-r--r-- 1 fraggod fraggod 465K Aug 22 19:03 test.7z
-rw-r--r-- 1 fraggod fraggod  48K Aug 22 19:03 test.tar.xz

Didn't realize that gz was that bad at such deduplication task.

Also somehow thought (and never really bothered to look it up) that 7z was compressing each file individually by default, which clearly is not the case, as overall size should be 10x of what 7z produced then.

Docs agree on "solid" mode being the default of course, meaning no easy "pull one file out of the archive" unless explicitly changed - useful to know.

Further 10x difference between 7z and xz is kinda impressive, even for such degenerate case.

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