AZ-104 Deploy and Manage Azure Compute Practice Question
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?
⚠ Common exam trap
Test-takers frequently choose Premium SSD for 'fastest boot' without realizing that ephemeral OS disks bypass network storage entirely, offering even lower latency for boot operations, and that the temporary disk cannot be used as an OS disk despite its local nature.
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
✓
An ephemeral OS disk
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.
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 Premium SSD managed OS disk
Why it's wrong here
Premium SSD managed OS disks are durable, high-performance remote storage, but they are persistent by design—the disk and its data remain in your subscription even after the VM is deleted, incurring ongoing storage costs. While they offer low latency and high IOPS, those benefits are wasted on a disposable weekly dev VM that does not require sustained performance. The remote nature of a managed disk also adds extra latency compared to a local ephemeral disk, making boot and OS disk operations slower despite the premium tier.
When this WOULD be correct
When the VM requires persistent OS disk data across deallocations and needs high performance for I/O-intensive workloads, such as a production database server that must retain OS state after shutdown.
- ✓
An ephemeral OS disk
Why this is correct
Ephemeral OS disks leverage local VM storage rather than a remote managed disk, placing the boot drive on the same host that runs the VM. This eliminates network round-trips for I/O, delivering significantly faster boot times and lower read/write latency. Because the dev VM is recreated from scratch every week, the lack of persistence is a benefit—each new VM gets a clean, empty OS disk, and there is no stale data or orphaned storage cost after deletion.
- ✗
A Standard SSD managed OS disk
Why it's wrong here
Standard SSD managed OS disks provide a balance of cost and durability, but they are still persistent managed disks that survive VM deletion, requiring manual cleanup and accruing storage charges when the VM is removed. Their moderate IOPS and throughput are inferior to both Premium SSD and ephemeral local disks, and because the OS disk is a remote disk, every boot and read/write operation traverses the storage network. For a VM recreated from scratch weekly, the persistent property is unnecessary and the slower boot time makes Standard SSD a poor fit.
When this WOULD be correct
When the VM requires persistent OS disk data across deallocations and reboots, and cost is a concern over performance, such as for a development VM that needs to retain state between sessions but does not require high IOPS.
- ✗
The VM temporary disk as the operating system disk
Why it's wrong here
The VM temporary disk (typically mounted as /mnt on Linux or D: on Windows) is not a supported location for the operating system. Azure only allows booting from a managed or unmanaged disk attached as the boot disk; the temporary disk is intended for page files, swap space, or transient application data. Its contents are not durable—they can be lost during a host maintenance event, a VM redeployment, or a stop/deallocate action—so it can never serve as the OS disk for a reliably recreatable VM.
When this WOULD be correct
If the question asked for a disk to store page files or temporary application data that can be lost without impact, and cost savings are prioritized, using the temporary disk would be correct.
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.
✓An ephemeral OS diskCorrect answer▾
Why this is correct
Ephemeral OS disks leverage local VM storage rather than a remote managed disk, placing the boot drive on the same host that runs the VM. This eliminates network round-trips for I/O, delivering significantly faster boot times and lower read/write latency. Because the dev VM is recreated from scratch every week, the lack of persistence is a benefit—each new VM gets a clean, empty OS disk, and there is no stale data or orphaned storage cost after deletion.
✗A Premium SSD managed OS diskWrong answer — click to see why▾
Why this is wrong here
Premium SSD managed disks persist data even after deallocation, which contradicts the requirement that OS disk contents do not survive deallocation. They also do not boot faster than ephemeral disks.
★ When this WOULD be the correct answer
When the VM requires persistent OS disk data across deallocations and needs high performance for I/O-intensive workloads, such as a production database server that must retain OS state after shutdown.
Why candidates choose this
Candidates often associate Premium SSD with 'fastest boot' and overlook the ephemeral disk option, not realizing that ephemeral disks are optimized for stateless, fast-boot scenarios.
✗A Standard SSD managed OS diskWrong answer — click to see why▾
Why this is wrong here
Standard SSD managed disks persist data even after deallocation, which contradicts the requirement that OS disk contents do not need to survive deallocation. Additionally, they are slower than ephemeral disks for boot performance.
★ When this WOULD be the correct answer
When the VM requires persistent OS disk data across deallocations and reboots, and cost is a concern over performance, such as for a development VM that needs to retain state between sessions but does not require high IOPS.
Why candidates choose this
Candidates may choose Standard SSD as a cost-effective compromise, not realizing that the question explicitly prioritizes boot speed and does not require persistence, making ephemeral disks the optimal choice.
✗The VM temporary disk as the operating system diskWrong answer — click to see why▾
Why this is wrong here
The VM temporary disk (D: drive on Windows, /dev/sdb on Linux) is not supported as an OS disk; it is intended for temporary data and is not bootable.
★ When this WOULD be the correct answer
If the question asked for a disk to store page files or temporary application data that can be lost without impact, and cost savings are prioritized, using the temporary disk would be correct.
Why candidates choose this
Candidates may confuse the temporary disk's fast, local storage with the ephemeral OS disk's purpose, thinking both provide similar speed and data loss tolerance.
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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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 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?
easy- A.Standard HDD managed disk
- ✓ B.Ephemeral OS disk
- C.Geo-redundant storage for the OS disk
- D.A data disk formatted as the boot disk
Why B: 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.
Variation 2. 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.
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.