DP-900 Practice Question: Describe considerations for working with non-relational data on Azure
Which THREE factors should you consider when choosing between Azure Blob Storage and Azure Cosmos DB for a new application? (Choose three.)
⚠ Common exam trap
DP-900 often tests whether candidates recognize that features common to both services (like encryption at rest) are not valid differentiators, so answers that list shared capabilities are distractors.
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
✓
Global distribution and multi-region writes
Option A is correct because Cosmos DB natively provides turnkey global distribution with multi-region writes across any Azure region, whereas Blob Storage replication options (LRS/ZRS/GRS/RA-GRS) do not offer writable multi-region endpoints, making this a key differentiator for globally distributed apps. Option B is correct because Blob Storage is designed for unstructured data (blobs, files, media) while Cosmos DB targets semi-structured JSON documents with a defined schema-less model, so the shape of the data drives the choice. Option E is correct because Cosmos DB supports rich querying via SQL, MongoDB, Gremlin, and Cassandra APIs with indexing, while Blob Storage only offers simple key-based access and limited querying through blob index tags. Option C is not a differentiator because both services encrypt data at rest by default using AES-256 (Storage Service Encryption and Cosmos DB encryption at rest), so it does not help choose between them. Option D is not a differentiator because both services offer very high scalability limits (Blob Storage scales to petabytes and high request rates; Cosmos DB scales to unlimited RU/s and storage), so scalability alone does not distinguish them.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Global distribution and multi-region writes
Why this is correct
Azure Cosmos DB is a globally distributed database service with turnkey multi-region replication and support for multi-region writes, ensuring low-latency writes and reads anywhere in the world. Azure Blob Storage is a single-region storage service that offers only asynchronous geo-redundant replication (GRS) and does not support active writes from multiple regions. This directly affects disaster recovery, availability, and user-perceived latency for globally distributed applications.
- ✓
Data structure (unstructured vs. semi-structured)
Why this is correct
Blob Storage is designed for unstructured data such as virtual machine disks, media files, and application backups, storing each item as an opaque binary blob with no schema or internal structure to query. Cosmos DB stores semi-structured JSON documents with flexible schemas, making it suitable for data with variable attributes and nested objects. Choosing between them depends on whether your data is a simple byte stream requiring only file-level access or structured content that needs document-level manipulation and relationships.
- ✗
Encryption at rest support
Why it's wrong here
Both Azure Blob Storage and Azure Cosmos DB encrypt data at rest by default, using Azure-managed keys with the option for customer-managed keys in both services. This equivalence means encryption at rest does not favor one service over the other and therefore is not a valid consideration when selecting between them. Security teams can satisfy compliance requirements equally with either option, so other factors like availability or querying must drive the decision.
- ✗
Scalability limits
Why it's wrong here
Azure Blob Storage can scale to exabytes by distributing blobs across storage partitions and storage accounts, while Azure Cosmos DB elastically partitions data across physical partitions and can scale throughput (request units per second) and storage independently and almost infinitely. Both services are designed to meet massive cloud-scale demands, so scalability limits rarely pose a distinction in practice. The decision should instead focus on the data shape and how it will be accessed.
- ✓
Query capabilities (simple key-value vs. complex queries)
Why this is correct
Blob Storage provides only REST-based key-value access to blobs and limited metadata filtering; it cannot query the content or structure of a blob itself. Cosmos DB offers a SQL-like query language, automatic indexing, and support for stored procedures, triggers, and user-defined functions over JSON documents, enabling complex ad-hoc queries and server-side logic. If your application requires rich queries, aggregations, or transactional consistency, Cosmos DB is clearly superior to Blob Storage.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
Go deeper
Related to this question
Learn chapter
Azure Cosmos DB
Key term
Schema
A schema is a blueprint or logical structure that defines how data is organized, stored, and accessed in a database or information system.
Key term
Encryption at rest
Encryption at rest is the practice of securing stored data by converting it into an unreadable format using cryptographic algorithms, so that even if physical or digital access to the storage medium is obtained, the data remains confidential.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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