Please contact your Quest Account Manager and request a quote for a license that include the necessary virtual capacity.
If VTL media is no longer needed, it can be removed from the NetVault database. On the Explore Storage screen, old virtual tapes will be listed. According to NetVault, the media still "exist" (they are just offline), and some of them could still have active savesets (i.e. due to expiration dates). The tapes need to be manually purge to get back within the licensing parameters. An illustration is attached.
