Hello
Ask away. On a basic level, it uses True Copy like technology to mirror writes between arrays before the acknowledgement is sent back to the host. Reads are services from either side. A great place to start regarding how it works, would be the Hitachi Vantara Knowledgebase:
https://knowledge.hitachivantara.com/Documents/Management_Software/SVOS/8.1/Global-Active_Device
The Overview page has some of the most common use cases and failure scenarios.
Regards
William