AZ-305 Design data storage solutions Practice Question
Your company, Contoso Ltd., is a global financial services firm with a primary data center in London and a disaster recovery site in Paris. They are migrating their on-premises SQL Server databases to Azure. The databases include: (1) a 2-TB customer database with high transaction throughput, requiring an RPO of 5 seconds and an RTO of 30 seconds; (2) a 500-GB reporting database that is read-only and can tolerate an RPO of 1 hour and an RTO of 2 hours; (3) a 100-GB archival database that is accessed once a month. The solution must minimize costs while meeting requirements. You need to recommend a storage and database strategy for each database. What should you recommend?
⚠ Common exam trap
A common mix-up: candidates assume all databases need the highest availability feature (active geo-replication) without considering cost optimization, or they mistakenly think Azure SQL Managed Instance can achieve sub-minute RPO, when in fact its auto-failover groups have a 5-minute RPO limit due to the use of distributed availability groups.
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
✓
Use Azure SQL Database with active geo-replication for the customer database, geo-restore for the reporting database, and long-term retention for the archival database.
It aligns the recovery objectives and cost constraints for each database. The customer database requires an RPO of 5 seconds and RTO of 30 seconds, which active geo-replication can meet by continuously replicating transactions to a secondary region with an RPO of 5 seconds and RTO of 30 seconds (including failover time). The reporting database tolerates an RPO of 1 hour and RTO of 2 hours, making geo-restore (which restores from geo-redundant backups with up to 1-hour RPO) a cost-effective choice. The archival database is accessed monthly, so long-term retention (LTR) backups stored in Azure Blob Storage minimize cost while meeting the infrequent access pattern.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Azure SQL Managed Instance for all databases with auto-failover groups.
Why it's wrong here
Azure SQL Managed Instance provides near-complete SQL Server engine compatibility and supports auto-failover groups for geo-disaster recovery, but that level of HA/DR is always-on, requiring higher minimum compute, storage, and licensing costs. Applying it uniformly to reporting and archival workloads forces you to pay for continuous geo-replication on data that does not need it; those databases can be restored from geo-redundant backups or retained via long-term retention at a fraction of the cost. Therefore, this approach is workable but is needlessly expensive and does not align recovery features with each workload's actual criticality.
- ✓
Use Azure SQL Database with active geo-replication for the customer database, geo-restore for the reporting database, and long-term retention for the archival database.
Why this is correct
Active geo-replication on the customer database continuously replicates transactions to a readable secondary in another region, giving you a low RPO and fast failover for the mission-critical transactional workload. Geo-restore for the reporting database uses geo-redundant backups to recover to another region only when a disaster occurs, avoiding the cost of maintaining a live secondary. Long-term retention on the archival database supports configurable backup retention up to ten years at blob storage pricing, satisfying compliance requirements without continuous replication. This tiered strategy pairs the right recovery and retention mechanism with each database's functional and cost requirements.
- ✗
Use Azure Cosmos DB for the customer database, Azure SQL Database for reporting, and Azure Blob Storage for archival.
Why it's wrong here
Cosmos DB is a globally distributed, multi-model NoSQL database, so using it for the customer database sacrifices relational features such as ACID transactions, T-SQL, and strict schema enforcement that financial services would typically require. Sending reporting traffic to Azure SQL Database while storing source data in Cosmos DB creates unnecessary impedance mismatches, forcing data movement and transformation in between. Likewise, Blob Storage for the archival database only gives you object storage, not the point-in-time restore or managed retention policies that Azure SQL's long-term retention offers. This mix therefore fails on relational integrity, integration complexity, and archival manageability.
- ✗
Use Azure SQL Database with active geo-replication for all databases.
Why it's wrong here
Putting active geo-replication on every database, including reporting and archival, means you are continuously provisioning and paying for a second replica in another region for each one, even when that data is rarely changing. The reporting database only needs disaster recovery to a secondary region occasionally, which geo-restore from geo-redundant backups can provide without consuming compute or storage 24/7. The archival database similarly needs long-term, compliance-grade backup retention, not live replication, so paying for geo-replicated secondaries is wasteful. This option would meet DR for the customer database but significantly exceeds the cost-benefit threshold for the other two workloads.
Quick reference
Azure Blob Storage Tier Comparison
| Tier | Storage Cost | Retrieval Cost | Latency | Use Case |
|---|---|---|---|---|
| Hot | Highest | Lowest | Immediate | Active data, frequent reads |
| Cool | Lower | Higher | Immediate | Data accessed < once / month |
| Cold | Lower still | Higher | Immediate | Data accessed < once / quarter |
| Archive | Lowest | Highest + rehydration delay | Hours | Long-term compliance retention |
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