AZ-104 Deploy and Manage Azure Compute Practice Question
A development VM is rebuilt often and does not need its operating system disk contents to survive deallocation. The team wants the lowest practical disk latency for the OS. Which disk option should the administrator choose?
⚠ Common exam trap
Candidates often choose Standard HDD (Option A) thinking it is the cheapest option, but they overlook that 'lowest practical disk latency' explicitly requires performance, not cost, and that Ephemeral OS disks provide both low latency and zero cost for the OS disk itself (since it uses local storage).
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 (SSD) rather than Azure managed disks, providing the lowest latency for OS read/write operations. Since the VM is rebuilt often and disk persistence is not required, the ephemeral disk is ideal because its contents are lost when the VM is deallocated, eliminating the need for a separate managed disk.
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 are persistent, network-attached storage that remain even after the VM is deleted, which is unnecessary for a development VM that is rebuilt often. They also rely on magnetic spinning disks, so I/O latency and throughput are far worse than the local NVMe-based ephemeral disk, adding a performance bottleneck to builds and application testing. Although the cost per GiB is low, you still pay for storage capacity and the disk state persists, so it does not address the 'does not need to persist' constraint.
When this WOULD be correct
If the question required a cost-effective solution for a VM that needs persistent OS disk data across deallocations and latency is not a primary concern, Standard HDD would be the correct choice.
- ✓
Ephemeral OS disk
Why this is correct
An ephemeral OS disk is hosted on the local VM storage instead of a managed disk, which eliminates the separate storage cost and dramatically reduces read/write latency. Because the disk is tied to the VM's lifecycle, every time the VM is deallocated or rebuilt the disk is reset to the original image, making it ideal for a frequently recreated development VM. This exactly matches the requirement that the VM does not need its OS disk to persist between runs.
- ✗
Geo-redundant storage for the OS disk
Why it's wrong here
Geo-redundant storage (GRS) replicates the OS disk to a paired Azure region to protect against regional outages, but that level of durability is pointless for a disposable dev VM that is rebuilt often. It does not improve local boot latency; in fact, the replication process adds no benefit to the VM's runtime I/O because the VM reads from the primary copy. Moreover, Azure managed OS disks default to locally redundant storage (LRS), and selecting GRS for a boot disk introduces extra cost and complexity while ignoring the real goal of fast, cheap, transient development environments.
- ✗
A data disk formatted as the boot disk
Why it's wrong here
Azure VMs always require a dedicated OS disk that contains the boot loader and operating system files; a data disk is attached separately and is meant for application or user data, not for hosting the OS. You cannot simply format a data disk as the boot disk because the VM's firmware is configured to boot from the OS disk, and modifying that would require custom image preparation and unattended setup. This approach violates Azure's standard disk architecture and would make an already frequently rebuilt VM even more complex to manage, so it is not a viable solution.
When this WOULD be correct
This option would be correct in a scenario where the question asks for a way to migrate an existing boot disk to a different storage type or to attach an existing VHD as a data disk for data recovery, not for the OS disk of a development VM.
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 diskCorrect answer▾
Why this is correct
An ephemeral OS disk is hosted on the local VM storage instead of a managed disk, which eliminates the separate storage cost and dramatically reduces read/write latency. Because the disk is tied to the VM's lifecycle, every time the VM is deallocated or rebuilt the disk is reset to the original image, making it ideal for a frequently recreated development VM. This exactly matches the requirement that the VM does not need its OS disk to persist between runs.
✗Standard HDD managed diskWrong answer — click to see why▾
Why this is wrong here
Standard HDD managed disks have higher latency compared to SSDs or ephemeral disks, and the question specifically asks for the lowest practical disk latency for the OS.
★ When this WOULD be the correct answer
If the question required a cost-effective solution for a VM that needs persistent OS disk data across deallocations and latency is not a primary concern, Standard HDD would be the correct choice.
Why candidates choose this
Candidates may default to Standard HDD as a familiar, low-cost option without considering that ephemeral OS disks offer even lower latency and are designed for stateless workloads.
✗A data disk formatted as the boot diskWrong answer — click to see why▾
Why this is wrong here
A data disk formatted as the boot disk cannot be used as the OS disk in Azure; the OS disk must be a managed disk attached as the OS disk, not a data disk. This option does not provide the lowest latency or meet the requirement for an OS disk that is rebuilt often.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the question asks for a way to migrate an existing boot disk to a different storage type or to attach an existing VHD as a data disk for data recovery, not for the OS disk of a development VM.
Why candidates choose this
Candidates might think that using a data disk as the boot disk could offer flexibility or cost savings, misunderstanding that Azure requires a specific OS disk type and that data disks cannot serve as the boot disk for a VM.
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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About these practice questions
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Same concept, more angles
2 more ways this is tested on AZ-104
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. 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?
medium- A.Standard HDD managed disk.
- B.Premium SSD managed disk.
- ✓ C.Ephemeral OS disk.
- D.Ultra Disk managed disk.
Why C: 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.
Variation 2. A development VM is recreated from scratch every week. The team wants the operating system disk to boot as quickly as possible and does not need the OS disk contents to survive deallocation. Which disk choice should the administrator make?
hard- A.A Premium SSD managed OS disk
- ✓ B.An ephemeral OS disk
- C.A Standard SSD managed OS disk
- D.The VM temporary disk as the operating system disk
Why B: An ephemeral OS disk is created on the local VM host storage, not on Azure managed storage, which eliminates network latency and provides significantly faster boot times. Since the team does not need the OS disk contents to survive deallocation and recreates the VM weekly, ephemeral disks are ideal as they are reset to the original image state on each deployment.
JA
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.