The correct answer is to enable Storage I/O Control (SIOC) on the NFS datastore and lower the latency threshold, as this directly addresses high latency without sacrificing capacity. SIOC works by monitoring the average latency of I/O operations against a user-defined threshold; when that threshold is exceeded, the hypervisor dynamically throttles the disk queues of the most I/O-intensive virtual machines, ensuring fair access to the shared NAS resource. On the VCP-DCV exam, this scenario tests your understanding of SIOC’s role in NFS environments—a common trap is assuming you must add more spindles or migrate to a different protocol, but SIOC’s latency-based algorithm proactively prevents congestion. Remember that reducing the latency threshold makes SIOC more sensitive, so it kicks in earlier to smooth out spikes. Memory tip: “Lower the bar, catch the lag” — a lower SIOC threshold catches latency earlier, keeping SQL servers responsive.
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 virtualized SQL server is experiencing high latency on its virtual disks. The datastore is an NFS mount on a shared NAS. Which action would most likely reduce disk latency without reducing capacity?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable Storage I/O Control (SIOC) on the datastore and set the latency threshold to a lower value.
D is correct because enabling Storage I/O Control (SIOC) on the NFS datastore and lowering the latency threshold allows the hypervisor to proactively throttle I/O-intensive VMs before the storage array becomes congested, reducing overall disk latency. SIOC uses a latency-based algorithm to enforce fairness and prevent a single VM from monopolizing I/O resources, which directly addresses the high-latency issue without altering the datastore capacity.
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.
✗
Increase the number of outstanding I/O requests per virtual disk in the VM settings.
Why it's wrong here
Incorrect: Increasing outstanding requests can increase queue depth and latency.
✗
Disable SIOC on the datastore to avoid overhead.
Why it's wrong here
Incorrect: Disabling SIOC removes I/O management, which can worsen latency under contention.
✗
Enable SIOC on the datastore and set the latency threshold to a higher value.
Why it's wrong here
Incorrect: A higher threshold reduces sensitivity, potentially increasing latency.
✓
Enable Storage I/O Control (SIOC) on the datastore and set the latency threshold to a lower value.
Why this is correct
Correct: SIOC actively manages I/O to reduce latency.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume increasing the latency threshold (Option C) will reduce latency by giving the storage more time, when in fact lowering the threshold forces earlier I/O throttling to prevent congestion.
Detailed technical explanation
How to think about this question
SIOC on NFS datastores works by monitoring the average latency of I/O commands sent to the NAS; when the latency exceeds the configured threshold (default 30 ms), SIOC begins to throttle the disk shares of VMs, queuing excess I/Os at the hypervisor level rather than letting them pile up at the storage array. Lowering the threshold (e.g., to 10 ms) triggers earlier intervention, which is beneficial for latency-sensitive workloads like SQL Server, but must be balanced to avoid excessive queuing that could reduce throughput. In real-world scenarios, NFS-based datastores often suffer from higher baseline latency due to network overhead, making SIOC tuning critical for performance.
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 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Enable Storage I/O Control (SIOC) on the datastore and set the latency threshold to a lower value. — D is correct because enabling Storage I/O Control (SIOC) on the NFS datastore and lowering the latency threshold allows the hypervisor to proactively throttle I/O-intensive VMs before the storage array becomes congested, reducing overall disk latency. SIOC uses a latency-based algorithm to enforce fairness and prevent a single VM from monopolizing I/O resources, which directly addresses the high-latency issue without altering the datastore capacity.
What should I do if I get this VCP-DCV 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: "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.
About these practice questions
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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. Which TWO options are valid methods to reduce vSphere storage latency? (Select two.)
medium
✓ A.Enable Storage I/O Control (SIOC).
✓ B.Increase the number of storage adapters.
C.Use VMFS-6 with automatic space reclamation.
D.Use larger block sizes in VMFS.
E.Use vSAN with deduplication and compression.
Why A: Correct: B (SIOC) and D (more storage adapters). SIOC prioritizes I/O to reduce latency for critical VMs. More storage adapters increase parallelism. Option A (space reclamation) helps efficiency but not latency. Option C (dedup/compression) may increase latency due to CPU overhead. Option E (larger block size) may help sequential but not reduce overall latency.
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This VCP-DCV practice question is part of Courseiva's free VMware 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 VCP-DCV exam.
Question Discussion
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