In ext[234]fs the reserved blocks is something else though: they are reserved to a specific user, by default root. So if normal users fill out the filesystem, t

In ext[234]fs the reserved blocks is something else though: they are reserved to a specific user, by default root. So if normal users fill out the filesystem, the root user still has some space to write. Sort of a simple quota system. I believe this problem in is only relevant to CoW filesystems. With ext[234]fs you can set the reserved blocks to 0, fill the fs, and always remove files to fix the situation.