NetApp has released SW integrated with main backup vendors' products to automate an existing manual process. When a virtual tape file on disk is written to tape a disk copy is actually kept. But the backup SW 'where is my backup file' function naturally lists the file as being on tape (and maybe shipped off-site). Canny Sysadms can actually - and manually - get it from disk (much faster than from tape) if a user needs that file to be restored.
Now NetApp has automated this so that the backup SW 'knows' the backup file is on tape but there is a shadow copy on disk. The disk copy will eventually be deleted because disk space fills up but now backup SW can automatically use disk copies of backup files shipped off to tape until they are actually deleted.
NetApp has responded to the general problem of which SW 'controls' the backup file location and restoration. Is it the backup SW or the virtual tape library SW? NetApp has enabled control to go back to the backup SW. Other VTL suppliers face the same problem.