C100DBA Sharding Practice Question
An application serves users in Europe and North America. The DBA wants to ensure that European user data stays on shards located in Europe to comply with data residency laws. Which feature should be used?
⚠ Common exam trap
Candidates often suggest using separate clusters for different regions. While possible, it is significantly more complex than using native MongoDB zones to manage data residency within one cluster.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Zones and Zone Ranges.
Zones (formerly known as tag-aware sharding) allow administrators to associate specific shard key ranges with particular shards. By tagging shards with geographical identifiers and defining zones for ranges of the shard key, the balancer will automatically move data to the appropriate physical location. This is essential for meeting regulatory requirements and reducing latency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replica set tags for read preferences.
Why it's wrong here
Replica set tags are used to route read operations to specific members within a single replica set based on their attributes. While useful for localizing reads, they do not control the physical storage location of data across multiple shards in a cluster, which is required for data residency compliance.
- ✓
Zones and Zone Ranges.
Why this is correct
Zones allow you to segment a sharded cluster based on shard key values. By assigning shards to zones (e.g., 'EU_Zone') and mapping specific key ranges to those zones, the balancer ensures that documents are stored only on the shards assigned to the matching zone, fulfilling data locality requirements.
- ✗
Hashed sharding with a geo-spatial index.
Why it's wrong here
Hashed sharding randomizes data distribution and is fundamentally incompatible with the goal of keeping specific data on specific shards. Geo-spatial indexes help with location-based queries but do not provide the administrative control needed to restrict data placement to specific physical hardware or geographic regions in a cluster.
- ✗
The movePrimary command for each database.
Why it's wrong here
The movePrimary command changes the default shard for all unsharded collections in a database. It cannot be used to distribute individual documents or ranges of a sharded collection based on their field values. Consequently, it is an inappropriate tool for managing granular data residency across multiple regions.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
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