Quick Answer
The answer is Azure Data Lake Storage Gen2 with Azure Synapse Serverless SQL. This combination is the most cost-effective for cold analytics data because ADLS Gen2 offers low-cost, scalable storage optimized for petabyte-scale data that is written once and rarely accessed, while Azure Synapse Serverless SQL enables on-demand SQL querying directly over the stored files without provisioning dedicated compute resources, eliminating idle costs. On the AZ-305 exam, this scenario tests your ability to match storage and compute services to data lifecycle patterns, specifically for cold data requiring long-term retention and occasional SQL-based analysis. A common trap is choosing Azure SQL Database or Cosmos DB, which are designed for transactional or warm data and become prohibitively expensive at petabyte scale. Remember the key principle: for cold analytics, separate cheap storage from serverless compute. Memory tip: “Cold data needs cold storage and hot-on-demand querying” — think ADLS for the icebox and Synapse Serverless for the occasional thaw.
This AZ-305 practice question tests your understanding of design infrastructure solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is designing a solution to store and analyze petabytes of IoT sensor data. The data is written once, rarely accessed, and must be retained for 10 years for compliance. The data must be queryable using SQL. Which combination of Azure services would be MOST cost-effective?
Azure Cosmos DB with analytical store
Why wrong: High cost for petabytes.
Azure SQL Database with Hyperscale tier
Why wrong: Expensive for cold data.
Azure Data Lake Storage Gen2 with Azure Synapse Serverless SQL
Cost-effective storage and SQL querying.
Azure Databricks with Delta Lake
Why wrong: More expensive for simple queries.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Azure Data Lake Storage Gen2 with Azure Synapse Serverless SQL
Option C is correct because Azure Data Lake Storage Gen2 (ADLS Gen2) provides low-cost storage for large volumes of data, and Azure Synapse Serverless SQL can query the data directly. Option A is wrong because Azure SQL Database is expensive for petabytes of cold data. Option B is wrong because Azure Cosmos DB is expensive for large cold storage. Option D is wrong because Azure Databricks is more expensive for simple SQL queries.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Azure Cosmos DB with analytical store
Why it's wrong here
High cost for petabytes.
Azure SQL Database with Hyperscale tier
Why it's wrong here
Expensive for cold data.
Azure Data Lake Storage Gen2 with Azure Synapse Serverless SQL
Why this is correct
Cost-effective storage and SQL querying.
Related concept
Static NAT maps one inside address to one outside address.
Azure Databricks with Delta Lake
Why it's wrong here
More expensive for simple queries.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related AZ-305 NAT questions on configuration and troubleshooting.
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FAQ
Design infrastructure solutions — This question tests Design infrastructure solutions — Static NAT maps one inside address to one outside address..
The correct answer is: Azure Data Lake Storage Gen2 with Azure Synapse Serverless SQL — Option C is correct because Azure Data Lake Storage Gen2 (ADLS Gen2) provides low-cost storage for large volumes of data, and Azure Synapse Serverless SQL can query the data directly. Option A is wrong because Azure SQL Database is expensive for petabytes of cold data. Option B is wrong because Azure Cosmos DB is expensive for large cold storage. Option D is wrong because Azure Databricks is more expensive for simple SQL queries.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related AZ-305 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
About these practice questions
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are designing a storage strategy for a data analytics solution that processes large volumes of streaming data. The data must be stored in a cost-effective manner with low latency for hot data and infrequent access for cold data after 30 days. The solution must support both batch and interactive queries. Which combination of Azure storage services should you recommend?
hardWhy A: Option B is correct because Azure Data Lake Storage Gen2 provides scalable storage for analytics with hierarchical namespace, and lifecycle management policies can move data to cool or archive tiers. Option A is wrong because Blob Storage with hot/cool tiers works but Data Lake Gen2 is optimized for analytics. Option C is wrong because Azure SQL Database is relational and expensive for large-scale analytics. Option D is wrong because Cosmos DB is for NoSQL workloads.
Last reviewed: Jun 20, 2026
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