Which option best describes a disadvantage (or cost) associated with database replication across sites?

Introduction / Context:
Replication provides benefits—availability, local read performance, and fault tolerance—but also introduces costs such as additional storage, administrative overhead, and potential consistency challenges.

Given Data / Assumptions:

• Replicas consume storage at multiple sites.
• Network coordination can be reduced for reads but still required for writes depending on model.
• The question frames one option as a disadvantage related to capacity.

Concept / Approach:
While strict equality of storage capacity is not a hard requirement in all systems, the downside captured by Option C reflects a practical cost: maintaining replicated copies increases storage demands across sites. In many exam contexts, this is presented as “every site must provision substantial storage for replicated data,” which is a disadvantage relative to a single copy.

Step-by-Step Solution:

Verification / Alternative check:
Operational experience shows storage and administrative overheads scale with the number of replicas; capacity planning becomes more complex.

Why Other Options Are Wrong:

• A: reduced network traffic for read-heavy workloads is an advantage, not a disadvantage.
• B: having a copy at another site is high availability (advantage).
• D: local autonomy (fewer coordinated transactions) is considered an advantage for performance and availability.

Common Pitfalls:
Assuming replication is “free” aside from setup; it impacts storage, write coordination, and conflict resolution.

Final Answer:
Each site must have the same storage capacity.