Creating an unused virtual tape produces an empty backing file. On the first write, and whenever later writes exceed the current allocation, Avanti extends the host file to the next 100 MiB boundary. This reduces incremental file growth and fragmentation. After a session records a write, closing or unloading the tape truncates the physical file length to the logical content length recorded during that session. Merely reopening and closing an existing tape without writing does not reconstruct a logical end from earlier sessions.