just saw from a comment of @PhoneBoy and interpretation of the website with images I can download...
There are 2 installation options:
fresh install with ISO/USB named "clean install" is the only way to add changes like file system e.g. ext3 to xfs.
But as we make a new system we also have a complete downtime. Its like a complete new install.
upgrade (in-place upgrade) no matter if it is clean install or upgrade, it does not change the file system but kernel should be changed also.
- clean install with CPUSE will not migrate the special configs e.g. kernel.conf
- upgrade with CPUSE will migrate all the configs
For Both there is a the Blink Image (Fast deployment) or a "normal" one, the blink has the latest hotfixes, the normal image almost has not hotfixes afaik.
Hope this is correct, whoever decided to use the term "clean install" for upgrade and also for real fresh install. Seeing repeating discussions in the community forum.