Free disk vs available disk

Deleting the filename doesn't actually delete the file. Some other process is holding the file open, causing it to not be deleted; restart or kill that process to release the file.

Use

lsof +L1

to find out which process is using a deleted (unlinked) file.

Check for files on located under mount points. Frequently if you mount a directory (say a sambafs) onto a filesystem that already had a file or directories under it, you lose the ability to see those files, but they're still consuming space on the underlying disk. I've had file copies while in single user mode dump files into directories that I couldn't see except in single usermode (due to other directory systems being mounted on top of them).