Lets start by assuming you’ve already installed mhvtl, you have a few virtual tape drives, a media changer, and a bunch of virtual tapes. You can control the media changer or library device at /dev/changer. Using MTX utilities, you can ask the changer to load tapes into drives and list map, etc. But i’ve found it’s actually easier for testing to control the drives directly. You can load and unload tapes directly into and out of a drive by barcode label and tape drive queue.