How do I delete a File?

Questions
1

Silverstripe Version: 4.2

Question:

How to delete a file from Database and Disk?
Why does deleteFile() returns false and deletes my file from Disk but not from Files Table?

function getDeleteOldAssets(){
		foreach(File::get()->sort(["FileFilename" => "ASC"]) as $f){
			$inUseCount = ($f->hasMethod('findOwners')) ? $f->findOwners()->count() : 0;
			if($inUseCount == 0) {
				if(!$f->deleteFile()){
					file_put_contents("notDeleted.log", "file not deleted: ".$f->ID." ".$f->FileFilename." nicht gelöscht"."\r\n", FILE_APPEND);
				}
			}
		}
	}
2

After deleting the file is it gone from the Files section of the CMS? Files are versioned in SS4 so while the file itself may be deleted, the database record is probably archived in the same way that Pages are. I guess.