Using a tar pair to move data between two systems, over an NFS link. This is faster than over ssh (ssh isn’t a fast transport layer).
Some user wrote a sparse file out.
An 11PB sparse file.
Which the tar happily … happily I tell you !!! was trying to copy, in its entirety, over to the backup unit.
Took me a quick look to see what was going on. It had copied 9TB of the 11PB file by the time I’d caught it.