AZ-204 Develop for Azure storage Practice Question
You need to upload large files (up to 100 GB) to Azure Blob Storage from a web application. The upload must be resilient to network failures and support pausing/resuming. Which approach should you use?
⚠ Common exam trap
A common mix-up: candidates confuse append blobs with block blobs, thinking append blobs support arbitrary uploads, but append blobs only allow data to be added to the end and cannot be used for random-access or parallel uploads.
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 block blob with multiple blocks and parallel upload.
Block blobs support uploading large files (up to ~4.75 TB) by splitting the file into multiple blocks, uploading them in parallel for speed, and committing the block list atomically. This approach provides resilience to network failures (individual blocks can be retried) and supports pausing/resuming by tracking which blocks have been uploaded.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upload the blob as a single PUT operation.
Why it's wrong here
Uploading a 100 GB file as a single PUT operation is not supported by Azure Blob Storage. The `Put Blob` REST API operation has a maximum size limit of 5 GB for a single blob upload (for API versions 2016-05-31 and later). Attempting to upload a file significantly larger than this limit will result in an error, and such an operation inherently lacks any built-in resumability or retry mechanisms, which are critical for large file transfers over potentially unstable networks.
- ✓
Use block blob with multiple blocks and parallel upload.
Why this is correct
Using block blobs with multiple blocks and parallel upload is the correct and recommended approach for uploading large files like 100 GB. This method involves breaking the large file into smaller, manageable blocks, which are then uploaded independently and potentially in parallel using `Put Block` operations. Once all blocks are successfully uploaded, a `Put Block List` operation commits them in the correct sequence to form the complete blob, providing robust resumability, retry capabilities, and significantly improved upload performance for very large files.
- ✗
Use append blob.
Why it's wrong here
Append blobs are specifically optimized for append operations, such as logging or auditing, where data is continuously added to the end of an existing blob. While they can grow to large sizes, they are not designed for the efficient, resumable initial upload of a complete, pre-existing large file from arbitrary chunks. There is no mechanism to commit blocks out of order or to resume a partially uploaded initial file in the same way block blobs facilitate, making them unsuitable for this scenario.
- ✗
Use AzCopy from the server.
Why it's wrong here
AzCopy is a powerful command-line utility and programmatic library (e.g., Go SDK) designed for high-performance data transfer to and from Azure Storage. While excellent for server-side or client-side *application* transfers, it is not a component that can be directly invoked or embedded within a client-side *web browser* for uploads. The question specifies uploading "from a web," implying a web application running in a browser, where AzCopy cannot be utilized for direct client-side file transfers.
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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Senior Network & Security Engineer · founder of Courseiva
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