Question 55 of 521

vSphere Performance and Scaling →hardMultiple ChoiceObjective-mapped

VCP-DCV vSphere Performance and Scaling Practice Question

This VCP-DCV practice question tests your understanding of vsphere performance and scaling. 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 managed hosting provider uses vSphere 7 with vSAN to run customer VMs. One customer's VM is a SQL Server database with 8 vCPUs and 128 GB RAM. The administrator notices that the VM's performance during peak hours is poor, with high disk latency and occasional disconnects. The cluster has 4 hosts, each with 10 cores (HT enabled) and 256 GB RAM. vSAN is configured with a hybrid disk group (SSD cache, HDD capacity) per host. The VM's storage policy is set to 'Performance' with RAID-1 mirroring (2 copies). The administrator runs esxtop and sees high %DAVG (device average latency) for the VM's vmdk. The observed latency averages 30 ms, but spikes to 100 ms. The host where the VM is running has relatively low CPU and memory usage, and the vSAN cache is not full. Which of the following is the most likely root cause and recommended solution?

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.

A
Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN.
Hybrid vSAN uses SSDs as cache and HDDs as capacity; write bursts can exceed the cache flush rate to HDDs, causing latency spikes. All-flash eliminates the HDD bottleneck.
B
Cause: vSAN cache is unable to handle the write burst. Solution: Add more cache capacity by using larger SSDs.
Why wrong: The cache is not full; the issue is write buffer exhaustion under burst, not capacity. Larger SSDs may not help if the burst exceeds cache write buffer.
C
Cause: The VM's memory ballooning is causing excessive swapping to vSAN, which is slow. Solution: Increase the VM's memory reservation.
Why wrong: Memory ballooning would cause high latency in swap I/O, but %DAVG is on the vmdk, not swap. Also, host memory is not overcommitted.
D
Cause: vSAN is encountering disk contention due to multiple VMs sharing the same disk. Solution: Deploy a dedicated vSAN datastore for the customer.
Why wrong: vSAN distributes objects across multiple disks and hosts, so sharing is inherent. A dedicated datastore does not change the architecture.

Full breakdown with real-world context →

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

✓

Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN.

The VM's high %DAVG spikes (up to 100ms) indicate that write bursts are overwhelming the single SSD cache in the hybrid disk group, forcing destaging to the slower HDD tier. The cache is not full (capacity is not the issue), so adding more cache (Option B) would not help; the problem is the write buffer exhaustion inherent to a single SSD cache. Memory ballooning (Option C) would cause swapping but would not directly cause high device latency; also the host has low memory usage, making ballooning unlikely. Disk contention from multiple VMs (Option D) is possible but not the most likely root cause given that the cache is not full and the latency spikes correlate with write bursts. Converting to all-flash vSAN (Option A) eliminates the HDD tier, providing consistent low latency even during heavy writes.

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.

✓
Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN.
Why this is correct
Hybrid vSAN uses SSDs as cache and HDDs as capacity; write bursts can exceed the cache flush rate to HDDs, causing latency spikes. All-flash eliminates the HDD bottleneck.
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.
✗
Cause: vSAN cache is unable to handle the write burst. Solution: Add more cache capacity by using larger SSDs.
Why it's wrong here
The cache is not full; the issue is write buffer exhaustion under burst, not capacity. Larger SSDs may not help if the burst exceeds cache write buffer.
✗
Cause: The VM's memory ballooning is causing excessive swapping to vSAN, which is slow. Solution: Increase the VM's memory reservation.
Why it's wrong here
Memory ballooning would cause high latency in swap I/O, but %DAVG is on the vmdk, not swap. Also, host memory is not overcommitted.
✗
Cause: vSAN is encountering disk contention due to multiple VMs sharing the same disk. Solution: Deploy a dedicated vSAN datastore for the customer.
Why it's wrong here
vSAN distributes objects across multiple disks and hosts, so sharing is inherent. A dedicated datastore does not change the architecture.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 practitioner preparing for the VCP-DCV exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

Quick reference

RAID Level Comparison

RAID Level	Min Disks	Fault Tolerance	Read	Write	Usable Capacity
RAID 0	2	None	Excellent	Excellent	100%
RAID 1	2	1 disk	Good	Moderate	50%
RAID 5	3	1 disk	Good	Moderate	67–94%
RAID 6	4	2 disks	Good	Lower	50–88%
RAID 10	4	1 disk per mirror	Excellent	Good	50%

RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.

What to study next

Got this wrong? Here's your next step.

Identify which VCP-DCV exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

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FAQ

Questions learners often ask

What does this VCP-DCV question test?

vSphere Performance and Scaling — This question tests vSphere Performance and Scaling — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Cause: vSAN disk group has a single SSD cache leading to high latency during heavy writes. Solution: Convert to all-flash vSAN. — The VM's high %DAVG spikes (up to 100ms) indicate that write bursts are overwhelming the single SSD cache in the hybrid disk group, forcing destaging to the slower HDD tier. The cache is not full (capacity is not the issue), so adding more cache (Option B) would not help; the problem is the write buffer exhaustion inherent to a single SSD cache. Memory ballooning (Option C) would cause swapping but would not directly cause high device latency; also the host has low memory usage, making ballooning unlikely. Disk contention from multiple VMs (Option D) is possible but not the most likely root cause given that the cache is not full and the latency spikes correlate with write bursts. Converting to all-flash vSAN (Option A) eliminates the HDD tier, providing consistent low latency even during heavy writes.

What should I do if I get this VCP-DCV question wrong?

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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