In Advanced Programming in the UNIX Environment (book) Section 4.14, interpret the i-node and directory, there is a paragraph:
When renaming a file without changing file systems, the actual contents of the file need not be moved--all that needs to be done is to add a new directory entry that points to the existing i-node and then unlink the old directory entry. For example, to rename the file
/usr/foo, the contents of the foo needn't be moved if the directories
/usrare on the same filesystem. This is how the
mvcommand usually operates.
According to that, a filename of a file should include the path to that file, and "mv" doesn't really move the file. But why the time it takes to move the two files under the same directory differs according to their size?