Sorry, for the very delayed and short response. I don’t often come on the forums and didn’t realize I left this question open. So to answer your question more fully.
You cannot have more than one GDDB per copy. Also, the GDDB must be unique to a Storage Policy as it cannot be utilized by more than one copy.
You could add the remote MA as an additional data path to the same disk library and add as a second partition to the GDDB but this would have very negative effects on regular backups as the performance would likely be drastically poor. Wouldn’t go down this path.
You could add additional data paths to the copy for remote MA for the same local disk library that do not host a DDB for the GDDB but if the primary MA hosting the GDDB fails then it needs to be restored or brought back up. The same could be done by adding another library as a data path to the GDDB but the same limitations apply. Blocks could be written across multiple locations and all would be required for a restore.
So with deduplication we need a minimum of two DDB partitions each on a local MA utilizing shared storage for the disk library to obtain a redundant solution. Ensure there is enough disk space to allow for additional blocks to be written temporarily if one of the partitions fails. Duplicate this at the other site and I think you will have a good solution.