On: Wipe and reinstall a running Linux system via SSH ...

[fulafel]

The amount of shrinkage available seems to be semi-random though, you can't shrink away all of the free space.

[Stratoscope → fulafel]

That will happen when there are unmovable files. There are a few tricks you can do to unlock some of these files, or you can use an external utility that you reboot into.

This article is from a vendor of such a utility, but it also describes how to unlock some of the unmovable files within Windows:

https://www.disk-partition.com/articles/shrink-volume-with-u...