The answer is an ephemeral OS disk, because it is stored directly on the local VM host rather than in Azure Storage, meaning it offers lower latency and is automatically deleted when the VM is deallocated. This makes it the perfect choice for stateless development VMs that are rebuilt often and do not need disk contents to survive deallocation. On the AZ-104 exam, this concept tests your understanding of the trade-off between persistence and performance—managed disks persist data but incur higher latency, while ephemeral disks sacrifice durability for speed and cost efficiency. A common trap is assuming all OS disks must survive deallocation; remember that ephemeral disks are ideal for temporary workloads like build agents or test environments. Memory tip: think “Ephemeral = Ephemeral existence” — if the VM stops, the disk vanishes.
AZ-104 Deploy and Manage Azure Compute Practice Question
This AZ-104 practice question tests your understanding of deploy and manage azure compute. 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.
Exhibit
Development environment notes:
- The VM is recreated frequently from an image
- The OS disk contents do not need to be preserved after the VM is deallocated
- The team wants the lowest practical OS disk latency
- Data durability is not the top priority for this VM
Based on the exhibit, which OS disk option best fits a development VM that is rebuilt often and does not need the disk contents to survive deallocation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Development environment notes:
- The VM is recreated frequently from an image
- The OS disk contents do not need to be preserved after the VM is deallocated
- The team wants the lowest practical OS disk latency
- Data durability is not the top priority for this VM
A
A Standard HDD managed OS disk.
Why wrong: Standard HDD is durable and low cost, but it does not provide the lowest practical latency for the OS disk.
B
An ephemeral OS disk.
An ephemeral OS disk is the best match because it provides very fast local storage for the operating system and does not need to preserve data after deallocation. This is ideal for rebuildable development VMs where performance matters more than retaining the OS disk contents.
C
A premium managed data disk used as the OS disk.
Why wrong: A managed data disk is not the normal choice for the operating system, and it adds complexity without meeting the requirement better than an ephemeral OS disk.
D
A shared disk attached to multiple VMs.
Why wrong: A shared disk is meant for specialized clustered workloads. It is not the right fit for a single development VM OS disk.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An ephemeral OS disk.
An ephemeral OS disk is created on the local VM host and not stored in Azure Storage, so it provides lower latency and is automatically deleted when the VM is deallocated. This makes it ideal for development VMs that are rebuilt often and do not require disk persistence across deallocations.
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.
✗
A Standard HDD managed OS disk.
Why it's wrong here
Standard HDD is durable and low cost, but it does not provide the lowest practical latency for the OS disk.
✓
An ephemeral OS disk.
Why this is correct
An ephemeral OS disk is the best match because it provides very fast local storage for the operating system and does not need to preserve data after deallocation. This is ideal for rebuildable development VMs where performance matters more than retaining the OS disk contents.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
A premium managed data disk used as the OS disk.
Why it's wrong here
A managed data disk is not the normal choice for the operating system, and it adds complexity without meeting the requirement better than an ephemeral OS disk.
✗
A shared disk attached to multiple VMs.
Why it's wrong here
A shared disk is meant for specialized clustered workloads. It is not the right fit for a single development VM OS disk.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume a Standard HDD managed disk is the cheapest option for a development VM, overlooking that ephemeral disks incur no storage cost and automatically reset the OS on each rebuild, which is more cost-effective and operationally simpler for the described use case.
Detailed technical explanation
How to think about this question
Ephemeral OS disks leverage the local SSD or NVMe storage of the Azure host, providing read/write performance comparable to locally cached disks but without the cost of managed disk storage. When the VM is deallocated or stopped, the disk is destroyed, and the next start creates a fresh OS disk from the specified image; this behavior is controlled by the 'DiffDiskPlacement' property set to 'CacheDisk' in the VM configuration. A real-world scenario is a CI/CD build agent that must start with a clean OS each time, avoiding leftover state or configuration drift.
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 AZ-104 question in full detail.
Deploy and Manage Azure Compute — This question tests Deploy and Manage Azure Compute — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An ephemeral OS disk. — An ephemeral OS disk is created on the local VM host and not stored in Azure Storage, so it provides lower latency and is automatically deleted when the VM is deallocated. This makes it ideal for development VMs that are rebuilt often and do not require disk persistence across deallocations.
What should I do if I get this AZ-104 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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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