Before the release of [Fedora 23](https://fedoramagazine.org/fedora-23-released/) I was working on a bug which have caused Anaconda to fail the installation because of RPM transaction check error. This brought me to the investigation of the required space check. It eventually lead to complete rework of the space requirement check in Anaconda. I would like to explain why this was needed and how is it working now.
#### The problem of the old space check The old solution was really minimalistic. It read installed size of all required packages from [DNF](http://dnf.baseurl.org/) Python interface and then added 35 percent as a 'bonus'. Why 35 percent? It is hard to tell. The number seems to be the result of some old empiric testing - too old to know for sure. And why to use 'bonus' at all? Because the value obtained from DNF is only a portion of space which is really needed for the installation. DNF computes installed package size as a sum of all file sizes in a package. It looks somewhat reasonable but it is sti