Depends. A Kubernetes container might have only a few megabytes of disk space, because it shouldn't need it.

Except that one time when .NET decides that the incoming POST is over some magic limit and it doesn't do the processing in-memory like before, but instead has to write it to disk, crashing the whole pod. Fun times.

Also my Unraid NAS has two drives in "WARNING! 98% USED" alert state. One has 200GB of free space, the other 330GB. Percentages in integers don't work when the starting number is too big :)

The "ballast file" idea doesn't really change that spill-to-disk crash, as far as I can tell. You have to delete it manually; it already crashed by the time you realize it.

Seems like the sort of thing that only makes sense in a "I know my cheapskate boss won't have larger drives ready to go (or be willing to pay to expand it in a cloud scenario), and he insists that the alarm not go off until 95%, but it'll be my fault if we have a bad incident we can't recover quickly from, so I'm gonna give myself some headroom by padding things a bit" extra-paranoid scenario.