Question 227 of 521

vSphere Performance and Scaling →mediumMultiple ChoiceObjective-mapped

NUMA Node Spanning Performance Impact — Remote Memory Access After DRS Migration

This VCP-DCV practice question tests your understanding of vsphere performance and scaling. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 company runs a critical application on a VM with 16 vCPUs and 128 GB RAM on an ESXi host that has 2 sockets (12 cores per socket, hyperthreading enabled) and 512 GB RAM. The application is known to scale well with multiple threads and memory bandwidth. Recently, a DRS migration moved the VM to a different host with the same CPU and memory configuration. After the migration, the application's performance dropped by 30%. The administrator checks vCenter and finds no other VMs on the destination host. esxtop shows the VM's CPU ready time is less than 1%, but the 'CPU cost' metric is high, and the 'Memory' section shows high values for 'Remote' memory accesses. What is the most likely cause of the performance drop?

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
The VM's virtual hardware version is not compatible with NUMA.
Why wrong: Most modern virtual hardware versions support NUMA properly.
B
The VM is spanning multiple NUMA nodes, causing remote memory access.
Spanning NUMA nodes increases memory latency, reducing application performance.
C
The VM's memory shares have been reduced after the migration.
Why wrong: Memory shares do not affect NUMA or memory locality.
D
Transparent Huge Pages are not enabled on the destination host.
Why wrong: While THP can affect performance, it is not the primary cause here; remote memory access is the more direct symptom.

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

✓

The VM is spanning multiple NUMA nodes, causing remote memory access.

The high 'Remote' memory access indicates that the VM's memory is being accessed from a NUMA node different from the one where the vCPUs are running. This occurs when a large VM spans multiple NUMA nodes. In this case, the VM has 16 vCPUs and the host has 2 NUMA nodes (each with 12 cores and hyperthreading). After DRS migration, the VM may be placed across both NUMA nodes, causing remote memory accesses and increasing the 'CPU cost' metric. This explains the 30% performance drop. Option B correctly identifies this cause. Option A (virtual hardware version) is not directly related. Option C (memory shares) affects prioritization, not remote access. Option D (Transparent Huge Pages) could affect performance but is not indicated by the metrics.

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.

✗
The VM's virtual hardware version is not compatible with NUMA.
Why it's wrong here
Most modern virtual hardware versions support NUMA properly.
✓
The VM is spanning multiple NUMA nodes, causing remote memory access.
Why this is correct
Spanning NUMA nodes increases memory latency, reducing application performance.
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.
✗
The VM's memory shares have been reduced after the migration.
Why it's wrong here
Memory shares do not affect NUMA or memory locality.
✗
Transparent Huge Pages are not enabled on the destination host.
Why it's wrong here
While THP can affect performance, it is not the primary cause here; remote memory access is the more direct symptom.

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.

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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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: The VM is spanning multiple NUMA nodes, causing remote memory access. — The high 'Remote' memory access indicates that the VM's memory is being accessed from a NUMA node different from the one where the vCPUs are running. This occurs when a large VM spans multiple NUMA nodes. In this case, the VM has 16 vCPUs and the host has 2 NUMA nodes (each with 12 cores and hyperthreading). After DRS migration, the VM may be placed across both NUMA nodes, causing remote memory accesses and increasing the 'CPU cost' metric. This explains the 30% performance drop. Option B correctly identifies this cause. Option A (virtual hardware version) is not directly related. Option C (memory shares) affects prioritization, not remote access. Option D (Transparent Huge Pages) could affect performance but is not indicated by the metrics.

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.

About these practice questions

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Same concept, more angles

1 more ways this is tested on VCP-DCV

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 small financial services company runs a critical trading application on a single vSphere host with two NUMA nodes (each with 8 cores). The VM is configured with 12 vCPUs and 64 GB memory. The application is not yet live, but load testing shows that CPU performance is satisfactory, but memory bandwidth is lower than expected. The application is known to benefit from fast memory access within a single NUMA domain. The administrator notices that the VM's memory is spread across both NUMA nodes. The administrator wants to force the VM to use only one NUMA node to maximize performance. However, the VM requires 12 vCPUs, which exceeds the 8 physical cores per node. What is the best course of action to improve memory bandwidth for this VM?

easy

A.Enable Hyper-Threading and reassign vCPUs to 12, and the VM will automatically run within one NUMA node.
✓ B.Keep the vCPU count at 12 but configure a NUMA Affinity to prefer the first NUMA node, and accept some cross-node memory access.
C.Keep the vCPU count at 12 but set CPU affinity to the first NUMA node only, leaving the second node unused.
D.Reduce the number of vCPUs to 8 to fit within one NUMA node, and keep the same memory size.

Why B: Option B is correct. NUMA affinity allows you to prefer a specific NUMA node for memory allocation. Even though the VM has 12 vCPUs exceeding the 8 cores per node, the VM will still run across both nodes for CPU, but memory will be preferentially allocated from the first NUMA node. This reduces cross-node memory access, improving memory bandwidth for the application. Option A is incorrect because enabling Hyper-Threading does not change the physical core count; 12 vCPUs still exceed 8 cores per node, and the VM cannot be placed entirely within one NUMA node. Option C is incorrect because setting CPU affinity to only the first NUMA node would restrict the VM to 8 cores, causing severe CPU contention and performance degradation. Option D is incorrect; reducing vCPUs to 8 may harm application performance if it requires more CPU resources, and the goal is to improve memory bandwidth while maintaining CPU capacity.

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