The answer is that the VM’s memory size forces it to span multiple NUMA nodes, increasing memory access latency. This occurs because each NUMA node on the host provides only 128 GB of memory, but the VM requires 256 GB; the hypervisor must allocate memory from both nodes, causing memory accesses to cross the NUMA interconnect (such as QPI or UPI), which introduces significantly higher latency than local memory access. On the ENCOR 350-401 exam, this scenario tests your understanding of how virtual machine sizing interacts with physical NUMA topology—a common trap is assuming more vCPUs or memory always improves performance, when in fact oversubscribing a single VM across NUMA nodes degrades it due to remote memory penalties. Remember the memory tip: “One node, one VM” to avoid NUMA spanning; if a VM’s memory exceeds a single node’s capacity, expect latency spikes and CPU ready time.
350-401 Virtual Machines and Hypervisors Practice Question
This 350-401 practice question tests your understanding of virtual machines and hypervisors. 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 network engineer is troubleshooting a VMware vSphere cluster where a VM with a large memory footprint (256 GB) is experiencing poor performance. The host has two NUMA nodes, each with 128 GB of memory. The VM is configured with 256 GB of memory and 4 vCPUs. Performance monitoring shows high memory latency and CPU ready time. What is the most likely cause?
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
✓
The VM's memory size forces it to span multiple NUMA nodes, increasing memory access latency.
The VM is configured with 256 GB of memory, but each NUMA node on the host has only 128 GB. Since a single NUMA node cannot satisfy the VM's memory allocation, the hypervisor must split the VM across both NUMA nodes. This forces memory accesses to cross the NUMA interconnect (e.g., QPI or UPI), which introduces significantly higher latency compared to local memory access, directly causing the observed high memory latency and increased CPU ready time.
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 memory size forces it to span multiple NUMA nodes, increasing memory access latency.
Why this is correct
Correct because when a VM's memory exceeds a single NUMA node, memory accesses cross nodes, causing higher 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.
✗
The VM has too few vCPUs for the memory size.
Why it's wrong here
Incorrect because vCPU count does not directly affect memory latency.
✗
The host is using memory ballooning to reclaim memory from other VMs.
Why it's wrong here
Incorrect because ballooning is a memory reclamation technique, not a cause of latency.
✗
The host's memory is overcommitted.
Why it's wrong here
Incorrect because the host has 256 GB total memory, matching the VM's allocation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that memory performance issues are always due to overcommitment or ballooning, but the trap here is that the VM's memory size exactly matches the total host memory, leading candidates to overlook the NUMA boundary constraint.
Detailed technical explanation
How to think about this question
NUMA (Non-Uniform Memory Access) architectures partition memory into nodes local to specific CPU sockets. When a VM's memory footprint exceeds a single NUMA node, the hypervisor (e.g., ESXi) must use interleaved or remote memory accesses, which traverse the interconnect at higher latency (e.g., 1.5x–2x slower). In vSphere, the VM's memory size and vCPU count determine whether the VM is treated as a 'wide' VM (spanning NUMA nodes) or a 'large' VM (requiring NUMA interleaving); the default behavior is to assign the VM to a single NUMA node if possible, but a 256 GB VM on dual 128 GB nodes forces a cross-node split.
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 350-401 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Virtual Machines and Hypervisors — This question tests Virtual Machines and Hypervisors — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VM's memory size forces it to span multiple NUMA nodes, increasing memory access latency. — The VM is configured with 256 GB of memory, but each NUMA node on the host has only 128 GB. Since a single NUMA node cannot satisfy the VM's memory allocation, the hypervisor must split the VM across both NUMA nodes. This forces memory accesses to cross the NUMA interconnect (e.g., QPI or UPI), which introduces significantly higher latency compared to local memory access, directly causing the observed high memory latency and increased CPU ready time.
What should I do if I get this 350-401 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.
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Question Discussion
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