This is to give you an idea to decide if your need this feature or not.


The IBM TS7700 Series is the latest in the line of tape virtualization products that has revolutionized the way mainframe customers utilize their tape resources. As older TS7700s sold since 2006 are looking to be refreshed in the field, the process of refreshing that hardware is becoming more difficult. There may be a few reasons that make the hardware refresh complicated:
-	Older levels of hardware may have limitations supported code levels.
-	More than three code levels are not supported in the same Grid.
-	Grid configurations are limited to six clusters total.
-	Grid merge requires all clusters be at the same code level.
Due to one or more of these limitations, upgrading to newer hardware, which often includes grid consolidation, can become difficult.  In addition, workloads are often needing to be moved between grid configurations, whether under the same client or at times between independent clients where workloads are acquired.  Host replication through a volume copy utility can be used in these cases, but not ideal. Therefore, the TS7700 solution needs a more flexible method to help with hardware and workload migration.  

Grid to Grid Migration (GGM) introduces a mechanism for two independent Grid configurations to intercommunicate for the purpose of replicating content from one Grid to another and addresses many of the migration issues described above. The two grid configurations rely on their existing Grid WAN/LAN networks be temporarily interconnected allowing grid volume replication techniques to copy data between grids.  A volume serial or VOLSER is retained through the migration process, though host catalog and Tape Management System (TMS) updates may also be required given the volume location has changed. Two major use-cases are supported.
•	Migration of logical volumes between grid configurations under the same system plex
•	Migration of logical volumes between grid configurations under independent system plexes.
Both methods require creation and/or updates of TCDB entries given all migrated volumes have changed library location.  TMS updates may also be required when content is moved between independent system plexes.

The GGM is supported when the source TS7700 Grid is R2.1 or later and the targert TS7700 Grid is R3.3 or later.  


So, if your decision is to use this - please go to the document "IBM® TS7700 Series. Grid To Grid Migration User’s Guide" to get full description about how it works.