[Gllug] Loopback mountable image file compression.

[Phillip Lougher]

James Laver <jjl <at> jameslaver.com> writes:


> Knoppix uses cloop, which takes their ~1.8GB image down to ~700mb ( so  
> I guess about 2.5x ). It's read-only and it's fully transparent (as a  
> kernel module).
> 
> I gather SquashFS is faster but less efficient at compression. 

Squashfs generally gets better compression than cloop (and is faster).
The webpage http://tree.celinuxforum.org/CelfPubWiki/SquashFsComparisons
gives some performance tests I made a couple of years ago for
SquashFS, Cloop, Cramfs and Zisofs.

>I've  
> noticed it's quite popular with non-knoppix liveCDs. There's also  
> SquashFS-lzma you should look out for but I've not tested it, I've no  
> idea about it's attributes or even it's stability.

There's third party LZMA patches available for Squashfs 3.3 (kernels
up to 2.6.29).  These won't work for Squashfs 4.0 (kernels 2.6.29 and
later).  I'm currently working on LZMA support for Squashfs 4.0.

The 3.3 LZMA patches are available from http://www.squashfs-lzma.org.
This page gives some statistics showing the better compression that
can be obtained using LZMA rather than GZIP.  The LZMA patches have
been in use for a number of years in various projects, and so they
should be stable.

Hope that helps.

Phillip




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