As you might know, I have this slight... thing... about backups. Due to the fact that during my working life, quite a few hard disk drives have gone under, so having a backup of stuff is really, really important for my peace of mind.
Which means, too, that periodically old backups need to be removed. That's something I always have a hard time with - but this time, it wasn't made hard by my internal resistance to deleting old files, no, it was made extra hard by Windows itself.
Before I swapped out one of the drives, I did a full copy to an external HDD, which means that a full, and theoretically run-able Windows installation resides on that disk. Which is not needed anymore, so I told my computer to delete it.
It didn't.
Turns out that the Windows files are not owned by me (even though logged in as the administrator), but by some straw figure thingie called "Trusted Installer". Who does not permit me to delete the stuff.
There's a workaround (of course there is), which makes it necessary to go into the security settings of the folder and swap the owner (to myself, of course). Which I tried to do, but suddenly, the disk was full... and it was not possible to change the settings anymore. Because, well, no space.
I am still confused as to how it could get fuller than before (there wasn't too much space left, but not next to nothing!) but I did manage to find a few things that I was allowed to delete, and now hopefully the owner swap will run its course, and I'll be able to make space again.
Oh Windows. I could have done without these shenanigans...