Ever wondered what is inside the TarMK's tar files? What is a segment and what is a record? How segment store garbage collection works and why (or why not)? This session will answer these questions and many more. It will shed light on the inner working of the TarMK, its system requirements and performance characteristics. It will help participants to better understand and diagnose the cause of common problems and present tools and techniques for diagnosing and debugging. Finally there will be a preview of what new features and enhancements we are currently working on.