> Hi,
>
> the 7-Zip archiver has recently become very popular because of
> its good compression rate;
> f.e. recent snapshot is about 34% smaller when packed with 7z
> compared to tar.gz:
>
> -rw-r--r-- 1 root root 2484981 Jan 5 17:28 openssl-SNAP-20080105.7z
> -rw-r--r-- 1 root root 3781438 Jan 5 17:27 openssl-SNAP-20080105.tar.gz


I'm not sure if the popularity of 7-Zip is high enough to justify the
effort. But the benefit is significant. I ran some tests of an OpenSSL build
using default settings for all compressors. It looked like this (higher is
better):

Tar: 1.0 (reference)
Tar+Compress: 2.7
Zip: 3.0
Tar+Zip: 4.9
Tar+GZip: 5.0
Tar+BZip2: 6.2
Tar+LRZ: 7.2
Tar+7-Zip: 7.3
7-Zip: 7.4

A 7-Zip download will be 15% faster (and use 15% less bandwidth) than a
BZip2 download and 1/3 faster than a GZip download.

7-Zip has an advantage over the other formats (except zip) in that it
combines compression with archiving, making it (at least in theory) easier
to manipulate the compressed archive. I'm not sure this matters anymore
given how fast typical computers are and how much memory they have compared
to the size of these files.

The real surprise (to me, anyway) is how bad zip did on its own. I believe
this is because zip compresses each file independently. This makes tar+zip
provide much better compression.

DS


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