Final answer:
Delta indexing is the monitoring input option that ignores a file's existing content and only indexes new data as it arrives.
Step-by-step explanation:
The monitoring input option that ignores a file's existing content and only indexes new data as it arrives is Delta indexing. Delta indexing is a process where only the changes or additions to a file are indexed, rather than re-indexing the entire file. This allows for more efficient indexing and reduces the need for re-indexing large files.