By default, a duplicate backup of a GRT set performs a copy to the destination, and then performs the catalog operation remotely. This is not practical in a WAN environment for performance reasons.
The registry key HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\Backup Exec for Windows\Backup Exec\Engine\Misc\DisablePDI2PDISetCopy can be used to alter the way that GRT backups are copied. Setting this value to 1 causes GRT backups to be copied in an MTF tape format for more efficient transport.
Granular restore of these sets is possible, but it requires staging the set on the media server during granular restore job execution.