The correct answer is that the service principal lacks the necessary permissions on the Data Lake Storage Gen2 endpoint (dfs.core.windows.net). This occurs because Azure Data Lake Storage Gen2 uses a hierarchical namespace and a separate DFS endpoint for data plane operations, distinct from the standard blob endpoint. Even with the Storage Blob Data Contributor role assigned, which grants permissions via the blob endpoint, the Spark job may be routing requests through the DFS endpoint, where the role assignment has not been properly propagated or applied. On the DP-900 exam, this scenario tests your understanding of how Azure Data Lake Storage Gen2 endpoints differ from Blob Storage, and it is a common trap where candidates assume a single role covers both endpoints. Remember the memory tip: "Blob for blobs, DFS for directories"—if your job hits the DFS endpoint, the role must be explicitly assigned at the storage account level for that endpoint to avoid access denied errors.
DP-900 Describe an analytics workload on Azure Practice Question
This DP-900 practice question tests your understanding of describe an analytics workload on azure. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 retail company uses Azure Data Lake Storage Gen2 as a data lake and Azure Databricks for ETL. They notice that a Spark job reading Parquet files from the data lake fails with an 'Access Denied' error when the job runs as a service principal. The service principal has Storage Blob Data Contributor role on the storage account. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service principal lacks the necessary permissions on the Data Lake Storage Gen2 endpoint (dfs.core.windows.net).
Option B is correct because Azure Data Lake Storage Gen2 uses a hierarchical namespace and a separate endpoint (dfs.core.windows.net) for data plane operations. Even though the service principal has the Storage Blob Data Contributor role (which grants read/write permissions via the blob endpoint), the job may be accessing the data through the DFS endpoint, which requires explicit permissions on that endpoint. The 'Access Denied' error typically occurs when the service principal is not granted the necessary RBAC role at the storage account level for the DFS endpoint, or when the role assignment is not properly propagated.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The service principal needs the Storage Blob Data Owner role instead.
Why it's wrong here
Data Contributor should be sufficient for read/write access.
✓
The service principal lacks the necessary permissions on the Data Lake Storage Gen2 endpoint (dfs.core.windows.net).
Why this is correct
The 'Access Denied' error occurs when using the DFS endpoint without proper RBAC assignment for that endpoint.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The storage account has a firewall enabled that blocks the Databricks cluster IP.
Why it's wrong here
No mention of firewall; the error points to permissions, not network.
✗
The service principal does not have the Storage Blob Data Contributor role assigned at the container level.
Why it's wrong here
The role at the storage account level should be inherited by containers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the Storage Blob Data Contributor role grants full access to all data plane operations, but they overlook that Azure Data Lake Storage Gen2 requires explicit permissions on the DFS endpoint for hierarchical namespace operations, which is a common point of failure in Spark-based ETL jobs.
Detailed technical explanation
How to think about this question
Azure Data Lake Storage Gen2 exposes two endpoints: the blob endpoint (blob.core.windows.net) and the DFS endpoint (dfs.core.windows.net). The DFS endpoint is required for operations that leverage the hierarchical namespace (e.g., directory-level operations, ACLs). When a Spark job reads Parquet files using the DFS endpoint, the service principal must have RBAC permissions that include the DFS endpoint; simply having the Storage Blob Data Contributor role on the storage account may not suffice if the role is not explicitly assigned to the DFS endpoint or if the service principal is not authenticated correctly for that endpoint. In practice, this often occurs when the service principal is not granted the 'Storage Blob Data Contributor' role at the storage account scope, or when the role assignment is not yet propagated to the DFS endpoint.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-900 question in full detail.
Describe an analytics workload on Azure — This question tests Describe an analytics workload on Azure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The service principal lacks the necessary permissions on the Data Lake Storage Gen2 endpoint (dfs.core.windows.net). — Option B is correct because Azure Data Lake Storage Gen2 uses a hierarchical namespace and a separate endpoint (dfs.core.windows.net) for data plane operations. Even though the service principal has the Storage Blob Data Contributor role (which grants read/write permissions via the blob endpoint), the job may be accessing the data through the DFS endpoint, which requires explicit permissions on that endpoint. The 'Access Denied' error typically occurs when the service principal is not granted the necessary RBAC role at the storage account level for the DFS endpoint, or when the role assignment is not properly propagated.
What should I do if I get this DP-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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