Restore old LTO4 after upgrade to LTO6 library

To summarise : You had 2 problems: 1) Inventory because barcode in the NBU Volume database had 6 characters but the new robot sees 8 and caused the 'not unique' error. This was fixed with vmchange command. 2) Restore is an issue because the density of LTO4 tapes and LTO6 are different. I prefer to change the density of a tape drive for the duration of the restore. There have been suggestions to change the density of the media. This will also work but NBU may now try to use the LTO4 tapes for backups, which will fail as LTO6 cannot write to LTO4. Rather keep LTO4 as different density to keep it separate and change tape drive density for restores. I have been able to change tape drive density without restarting Device Manager service.