AZ-305 Design data storage solutions Practice Question
Contoso Ltd. is a global retail company with headquarters in New York and operations in Europe and Asia. They are migrating their on-premises SQL Server databases to Azure. The databases include a customer database (500 GB), an orders database (2 TB), and a product catalog database (100 GB). The customer database requires high read throughput with sub-10 ms latency for global users. The orders database must support complex queries and reporting with point-in-time restore capability up to 35 days. The product catalog is updated infrequently but must be available for read-heavy workloads with strong consistency. Contoso wants to minimize costs while meeting performance and compliance requirements. They also need to support hybrid deployments for databases that must remain on-premises due to data sovereignty laws. You need to design a data storage solution. Which combination of Azure services and configurations should you recommend?
⚠ Common exam trap
A common mix-up: candidates assume Azure SQL Database Hyperscale is a one-size-fits-all solution for large databases, overlooking its limitations with point-in-time restore duration and complex query performance, and fail to recognize that Cosmos DB is the only Azure service designed for global low-latency reads with multiple write regions.
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
✓
Azure Cosmos DB with multiple write regions for customer DB; Azure SQL Database Business Critical for orders; Azure SQL Database serverless for product catalog; Azure SQL Managed Instance with managed instance link for hybrid
It matches each database's workload to the optimal Azure service: Cosmos DB with multiple write regions provides global low-latency reads and writes for the customer DB; Azure SQL Database Business Critical offers the complex query support and point-in-time restore up to 35 days for the orders DB; Azure SQL Database serverless minimizes cost for the infrequently updated product catalog; and Azure SQL Managed Instance with managed instance link enables hybrid deployment for on-premises databases subject to data sovereignty laws.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Azure SQL Managed Instance for all databases with geo-replication for customer DB; use failover groups for global distribution; Azure Data Sync for hybrid
Why it's wrong here
Azure SQL Managed Instance lacks a multi-region writable architecture; geo-replication and failover groups provide only an asynchronous, read-only secondary in another region, with RPO potentially reaching seconds, so customer database reads and writes outside the primary region will not see sub-10 ms latency. Additionally, Azure SQL Data Sync does not support Managed Instance as a sync member, which makes the proposed hybrid plan invalid; the correct cloud-to-on-premises replication mechanism for Managed Instance is the managed instance link, not Data Sync.
- ✗
Azure SQL Database Hyperscale for all databases; use geo-replication for customer DB; Azure SQL Server on Azure VMs for hybrid
Why it's wrong here
While Azure SQL Database Hyperscale decouples storage from compute and can scale a very large database, it still has a single writable primary and only supports asynchronous geo-replication for disaster recovery, so it cannot provide active-active sub-10 ms latency across worldwide regions. Using SQL Server on Azure VMs for hybrid is also a mismatch: it is an IaaS migration target, not a data synchronization bridge to existing on-premises SQL Server; the managed instance link is the Azure-native hybrid replication feature, not IaaS virtual machines.
- ✓
Azure Cosmos DB with multiple write regions for customer DB; Azure SQL Database Business Critical for orders; Azure SQL Database serverless for product catalog; Azure SQL Managed Instance with managed instance link for hybrid
Why this is correct
Azure Cosmos DB with multiple write regions gives every regional endpoint the ability to accept reads and writes with single-digit millisecond latency, enabling the global customer database to meet sub-10 ms performance through multi-homing and tunable consistency. Business Critical tier for orders provides SQL Server-compatible T-SQL, ACID transactions, and low-latency local Always On availability, which is appropriate for complex order queries and strict transactional guarantees. Serverless product catalog avoids fixed compute costs for an intermittently queried reference dataset, while Managed Instance with the managed instance link provides near-real-time bidirectional replication between Azure and existing on-premises SQL Server to satisfy the hybrid footprint.
- ✗
Azure SQL Database Business Critical for customer DB with geo-replication; Azure SQL Database Hyperscale for orders; Azure SQL Database serverless for product catalog; Azure SQL Managed Instance for hybrid
Why it's wrong here
Placing the customer database in Business Critical tier with geo-replication still leaves only one writable regional endpoint; the geo-replica is asynchronous and not used for writes, so users on other continents will not receive sub-10 ms write latency and may even see stale reads during replication lag. Hyperscale for orders does not fix this global consistency problem and introduces unnecessary architectural complexity, and simply saying Managed Instance for hybrid misses the managed instance link requirement that actually enables online transactional replication from an on-premises SQL Server instance.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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