Best Practice for File stub size? File size seems the same after purging

Hi all, very familiar with DX for Windows and now doing my first DX for Linux (RHEL 4) and a few things have me confused. 1.) In the manual it suggests an ls -ls before and after a move/purge will show the difference in the stub file size before and after, however I show the same size. df -h shows less space consumed on the filesystem. How do I prove a file was successfully stubbed and retrieved from Centera without this data?

2.) getfilestubsize and setfilestubsize commands are referenced in the manual do not seem to exist in my install.

3.) It seems strange to me coming from DX Win that you would be able to set the stub file size. What is the best practice/rule of thumb for size, and what are the effects of having it too small/too large? I left it at the default of 0 to start with.