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BuntuSeriously
Asked: 2013-08-08 07:18:24 +0800 CST

Why is full compression not used during squash?

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Was interested to know why, with space/bandwidth at such a premium, is full compression not used during squash.

For example, calling mksquashfs with the -comp xz -b 1M options at compression time creates an archive which weighs in at about 80% of the original filesystem.squashfs; yet appears to retain full integrity as both an installation and live image.

Does anybody have some intel here?

squashfs

1 Answers

  1. Presumably because xz (LZMA) compression requires disproportionately more CPU time for both compression and decompression, something that does make a difference when loading the system from a live USB stick, for instance. See a wider discussion of xz vs gzip on Stack Overflow.

    In a similar vein, there is an open blueprint for using xz to compress packages in the Ubuntu archive. This appears to be on hold for the moment on the basis it offers relatively little benefit.

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