Squashfs-LZMA.org

SquashFS version 4 is included in Linux Kernel since 2.6.29 and it supports XZ (LZMA2) compression since 2.6.38. What does it mean for this project (squashfs-lzma.org)? There is no longer any need to use external patches, so this project is discontinued. You can happily mount your newly created squashfs images directly with recent kernel! :) This website will remain with slight updates for reference.

LZMA is one of the best compression algorithms and Squashfs is one of the best compressed filesystems available nowadays. This project combined both to make something even better. LZMA can compress much better then gzip, which was the only option in squashfs for years. Compressing to LZMA format is very slow, but this is not a problem as the squashfs filesystem needs to be compressed only once. Then it's only read million times; so what we care about is the speed of decompression. LZMA decompression is slower than gzip, but it's even very fast, about 10-20 MB/s on a 2GHz CPU.

method	block size	Slax data size	percent
uncompressed	-	668 MB	100%
mksquashfs+gzip	64KB	227 MB	34%
mksquashfs+gzip	1024KB	222 MB	33%
mksquashfs+lzma	64KB	191 MB	28%
mksquashfs+lzma	128KB	184 MB	27%
mksquashfs+lzma	512KB	172 MB	26%
mksquashfs+lzma	1024KB	167 MB	25%

Squashfs' author couldn't support LZMA directly in squashfs source code. He wanted to have the squashfs code included in official Linux Kernel, but Linux Kernel didn't support LZMA/XZ at that time, so adding LZMA to squashfs would decrease the chance for its (squashfs's) inclusion. This was the main reason we had to maintain LZMA support as a separate patch.

As already said, recent squashfs doesn't need any patches neither to kernel nor to the tools. Simply download squashfs tools v4.x from the link at the top left sidebar, extract, edit Makefile to add XZ support by uncommenting XZ_SUPPORT = 1, and run make && make install. Then you can compress your files using for example:

mksquashfs source1 dest.sqfs -comp xz -b 262144
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