ISO image: to xz or not to xz?

[Ludovic Courtès]

Hi!

Here’s the installation ISO image (with built-in zlib compression):

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix system image -t iso9660 gnu/system/install.scm
/gnu/store/kg63cyg94dmy9x7rpxf5ycn97sqx1ndl-image.iso
$ xz < /gnu/store/kg63cyg94dmy9x7rpxf5ycn97sqx1ndl-image.iso > /tmp/t.iso.xz
$ du -h /tmp/t.iso.xz
496M    /tmp/t.iso.xz
$ du -h /gnu/store/kg63cyg94dmy9x7rpxf5ycn97sqx1ndl-image.iso
647M    /gnu/store/kg63cyg94dmy9x7rpxf5ycn97sqx1ndl-image.iso
--8<---------------cut here---------------end--------------->8---

The xz-compressed image is 23% smaller, which is not negligible.
However, it’s apparently quite unusual to distribute compressed ISOs and
some services/tools such as libosinfo require plain ISOs (uncompressed).

Should we distribute the installation ISO without xz compression?

That could be done in respect of the string freeze (removing text, not
modifying it), though the relevant section would look odd because it’d
have a single step (info "(guix) USB Stick and DVD Installation").

Or maybe it’s safer to postpone that question until the next release.

What do people think?

Ludo’.