AdvFS determines this by examining the status of the clone's metadata. The file was created after the clone was created and is not part of the clone fileset. Nothing is done to the clone fileset. Metadata exists and the data has been marked as saved. This is not the first update to this page of the file.
Nothing is done to the clone fileset.
Metadata exists but this page has not been marked as saved. This is the first change to this page of the file. Original data is being updated. Metadata for this page of the clone is altered and the page marked as saved. Disk space is allocated in the clone fileset and the original data is copied into the new space.