What is Cassandra multi-datacenter architecture and geo-distribution?

Cassandra's multi-datacenter architecture is a first-class feature, not an afterthought. Configure with NetworkTopologyStrategy: WITH replication = {'class': 'NetworkTopologyStrategy', 'us-east': 3, 'eu-west': 3}. Consistency across DCs: use LOCAL_QUORUM for operations — quorum within the local DC, async replication to remote DCs. Avoids cross-DC round trips for every operation. LOCAL_ONE: maximum local speed, highest staleness risk. EACH_QUORUM: quorum in every DC — strong global consistency, higher latency. Write path: coordinator writes to local DC synchronously (based on consistency level), and sends the write asynchronously to remote DCs. Remote DC writes are guaranteed to eventually succeed via hinted handoff and repair. Active-active multi-DC: users in each region write to their local DC — both DCs accept writes. Conflicts resolved by LWW. Active-passive: one DC is the primary writer, remote DC is a warm standby. Multi-DC Cassandra is the architecture of choice for global applications requiring local latency, data locality compliance (GDPR), and regional failover.