LTO7 is not recognized under Windows Server 2012 and 2012 R2. The device appears as unknown in the device manager.
This article provides a workaround to manually install the driver to have the LTO7 correctly displayed under Windows 2012.
LTO7 is not supported under Windows Server 2008, update to Windows 2012 is needed.
1) Install HBA adapter/controller firmware. The package file can be download on the LTO-7 download page
2) Install the Windows hotfix https://support.microsoft.com/en-us/kb/3095711
(external link) : Update to support LTO-7 tape drives in Windows Server
3) Install LTO7 driver using the package install_nonexclusive.exe