AZ-104 Deploy and Manage Azure Compute Practice Question
A development environment uses temporary test VMs that can be rebuilt at any time. The administrator wants the operating system disk to provide the lowest practical latency and does not need the disk data to survive a deallocate operation. Which OS disk option should be selected?
⚠ Common exam trap
Test-takers frequently choose Premium SSD (B) because they associate 'lowest latency' with premium managed disks, forgetting that ephemeral OS disks use local storage which is inherently faster and also meets the 'no persistence' requirement, while managed disks always persist data across deallocations.
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
✓
Ephemeral OS disk.
Ephemeral OS disks use the local VM storage (temporary disk) rather than remote managed storage, which provides the lowest possible latency because data is stored directly on the host node. Since the test VMs can be rebuilt at any time and the disk data does not need to survive a deallocate operation, the ephemeral disk is ideal—it is automatically deleted when the VM is deallocated or deleted, and it avoids the cost and performance overhead of managed disks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Standard HDD managed disk.
Why it's wrong here
Standard HDD managed disks rely on magnetic spinning media, delivering far lower IOPS and higher latency than SSD-backed options, so they would make a temp test VM perform poorly even during short-lived use. They are also persistent network-attached storage: when the VM is deallocated, the disk stays in Azure Storage and continues to incur meter charges. Thus, the frugal price point is outweighed by both sluggishness and the hassle of manual cleanup for transient workloads.
When this WOULD be correct
A scenario where cost is the primary constraint and performance requirements are minimal, such as for archival or backup storage where low cost is prioritized over latency, and data persistence is needed across VM deallocations.
- ✗
Premium SSD managed disk.
Why it's wrong here
Premium SSD managed disks are network-attached storage backed by Azure's enterprise-grade SSDs, offering high IOPS and low latency for production workloads. Unlike an ephemeral OS disk, a Premium SSD remains durably persisted in Azure Storage after the VM is stopped or deallocated, so temporary test VMs incur ongoing storage costs and leave orphaned VHDs that must be manually deleted. For a disposable dev environment, the persistence is unnecessary overhead.
When this WOULD be correct
When the question requires persistent OS disk data across deallocate operations and the workload demands high IOPS and low latency, such as for a production database VM that must retain its OS state after being stopped.
- ✓
Ephemeral OS disk.
Why this is correct
Ephemeral OS disks are designed specifically for stateless workloads like temporary test VMs. The disk is hosted on the local VM storage rather than Azure Storage, providing the lowest possible read/write latency for the OS. When the VM is stopped, deallocated, or redeployed, the disk content is lost, which is exactly what you want for disposable test environments—no persistent storage cost or orphaned disks to clean up.
- ✗
Ultra Disk managed disk.
Why it's wrong here
Azure Ultra Disk offers extremely high IOPS and sub-millisecond latency, but it is intended for data disks on IOPS-intensive workloads like large databases—it is not supported as an OS disk for a VM at all. Even if it were, its persistent storage and premium price would make it absurdly overprovisioned for a disposable test VM that needs only temporary local storage. This makes it the opposite of the lightweight OS disk required here.
When this WOULD be correct
When the question asks for the highest performance managed disk for a critical database workload that must persist data across VM restarts and deallocations, and cost is not a primary concern, Ultra Disk would be the correct choice.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-104 exam frequently reuses these exact scenarios with slightly different constraints.
✓Ephemeral OS disk.Correct answer▾
Why this is correct
Ephemeral OS disks are designed specifically for stateless workloads like temporary test VMs. The disk is hosted on the local VM storage rather than Azure Storage, providing the lowest possible read/write latency for the OS. When the VM is stopped, deallocated, or redeployed, the disk content is lost, which is exactly what you want for disposable test environments—no persistent storage cost or orphaned disks to clean up.
✗Standard HDD managed disk.Wrong answer — click to see why▾
Why this is wrong here
Standard HDD managed disks have the highest latency among Azure disk types, which contradicts the requirement for the lowest practical latency. Additionally, they are persistent and survive deallocation, which is unnecessary for temporary VMs that can be rebuilt.
★ When this WOULD be the correct answer
A scenario where cost is the primary constraint and performance requirements are minimal, such as for archival or backup storage where low cost is prioritized over latency, and data persistence is needed across VM deallocations.
Why candidates choose this
Candidates may mistakenly think Standard HDD is sufficient for temporary VMs due to its low cost, overlooking the explicit latency requirement and the availability of Ephemeral OS disks for non-persistent, high-performance needs.
✗Premium SSD managed disk.Wrong answer — click to see why▾
Why this is wrong here
Premium SSD provides low latency but its data persists through deallocate, which contradicts the requirement that disk data does not need to survive deallocate. Ephemeral OS disk is the correct choice for lowest latency and data loss on deallocate.
★ When this WOULD be the correct answer
When the question requires persistent OS disk data across deallocate operations and the workload demands high IOPS and low latency, such as for a production database VM that must retain its OS state after being stopped.
Why candidates choose this
Candidates associate Premium SSD with low latency and high performance, overlooking the specific requirement that data does not need to survive deallocate, which makes Ephemeral OS disk the better fit.
✗Ultra Disk managed disk.Wrong answer — click to see why▾
Why this is wrong here
Ultra Disk provides extremely low latency, but it is a managed disk that persists data through deallocate operations and is not ephemeral. The question requires the disk to not survive deallocation, so Ultra Disk does not meet that requirement.
★ When this WOULD be the correct answer
When the question asks for the highest performance managed disk for a critical database workload that must persist data across VM restarts and deallocations, and cost is not a primary concern, Ultra Disk would be the correct choice.
Why candidates choose this
Candidates see 'lowest practical latency' and immediately think of Ultra Disk, which is indeed the lowest-latency managed disk option, but they overlook the requirement that the disk data must not survive a deallocate operation.
Analysis generated from the official AZ-104blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-104 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-104 exam.