Question $1$: You are tasked with designing a distributed storage system for a cloud$-$based application that serves millions of users worldwide. The system must ensure high availability, fault tolerance, and efficient data replication across multiple data centers located in different continents. Describe how you would incorporate redundancy mechanisms at both the node and data levels to mitigate the impact of node failures and data loss. Discuss the implementation of proactive failure handling strategies, such as automatic failover and checkpointing, to ensure data consistency and integrity. Furthermore, explore the role of advanced communication models like multicast and scatter$-$gather in optimizing data replication and synchronization processes across distributed nodes.