- A
Enable vNUMA for both VMs to improve memory access, and set CPU affinity to dedicate specific cores.
Why wrong: Incorrect. vNUMA helps with memory locality, not CPU ready time or storage latency; CPU affinity reduces scheduler flexibility.
- B
Increase the RAM for both VMs to reduce disk swapping, and enable Hyperthreading on the ESXi host.
Why wrong: Incorrect. RAM increase does not address CPU ready time or NFS latency; Hyperthreading may even worsen contention.
- C
Reduce the number of vCPUs assigned to App-2 from 8 to 4, and configure Storage I/O Control on the datastore.
Correct. Reducing vCPUs decreases CPU ready time; Storage I/O Control manages disk latency.
- D
Migrate the VMs to another ESXi host with faster CPUs, and upgrade the storage network to 10 Gbps.
Why wrong: Incorrect. While migration might help, it is disruptive and does not address root cause of oversubscription; storage network upgrade alone won't fix CPU ready time.
Quick Answer
The answer is to reduce App-2’s vCPUs from 8 to 4 and enable Storage I/O Control (SIOC) on the NFS datastore. This directly addresses both VMware vSphere CPU ready time and disk latency optimization: App-2’s 8 vCPUs exceed the host’s 8 physical cores per socket, causing co-scheduling contention that inflates App-1’s CPU ready time to 15%, while SIOC prioritizes disk access during congestion, cutting the 50 ms latency by enforcing shares and limits on the shared NFS datastore. On the ENCOR 350-401 exam, this scenario tests your understanding of CPU overcommitment ratios and storage QoS mechanisms—a common trap is to assume adding hardware (e.g., faster storage or more cores) is the fix, when the real issue is misconfigured virtual resources. Remember the “core-per-socket rule”: never assign more vCPUs to a VM than physical cores per socket on the host, or ready time spikes. For disk latency, think “SIOC saves the clock”—it throttles low-priority I/O before latency climbs.
350-401 Virtualization Practice Question
This 350-401 practice question tests your understanding of virtualization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 financial company runs a critical trading application in a virtualized environment on VMware vSphere. The application consists of two VMs: App-1 (web server) and App-2 (database server). Both VMs are on the same ESXi host. Recently, users report intermittent slowness during peak trading hours. Monitoring shows that App-1 experiences high CPU ready time (up to 15%) and App-2 has high disk latency (average 50 ms). The ESXi host has 16 vCPUs total (2 sockets, 8 cores each) and 128 GB RAM. The host runs 10 VMs total. App-1 has 4 vCPUs and 16 GB RAM; App-2 has 8 vCPUs and 32 GB RAM. The storage is a shared NFS datastore connected via 1 Gbps Ethernet. The network is 10 Gbps. What is the MOST effective course of action to resolve the performance issues?
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
Reduce the number of vCPUs assigned to App-2 from 8 to 4, and configure Storage I/O Control on the datastore.
Option C is correct because App-2's 8 vCPUs exceed the number of physical cores per socket (8), causing CPU scheduling contention and high ready time on App-1, while reducing vCPUs to 4 aligns with the host's core-per-socket count and reduces co-scheduling overhead. Additionally, Storage I/O Control (SIOC) on the NFS datastore can prioritize disk access and mitigate the high disk latency (50 ms) by enforcing shares and limits during congestion, addressing both performance issues without requiring hardware upgrades.
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.
- ✗
Enable vNUMA for both VMs to improve memory access, and set CPU affinity to dedicate specific cores.
Why it's wrong here
Incorrect. vNUMA helps with memory locality, not CPU ready time or storage latency; CPU affinity reduces scheduler flexibility.
- ✗
Increase the RAM for both VMs to reduce disk swapping, and enable Hyperthreading on the ESXi host.
Why it's wrong here
Incorrect. RAM increase does not address CPU ready time or NFS latency; Hyperthreading may even worsen contention.
- ✓
Reduce the number of vCPUs assigned to App-2 from 8 to 4, and configure Storage I/O Control on the datastore.
Why this is correct
Correct. Reducing vCPUs decreases CPU ready time; Storage I/O Control manages disk latency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Migrate the VMs to another ESXi host with faster CPUs, and upgrade the storage network to 10 Gbps.
Why it's wrong here
Incorrect. While migration might help, it is disruptive and does not address root cause of oversubscription; storage network upgrade alone won't fix CPU ready time.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that adding more vCPUs always improves performance, but the trap here is that over-provisioning vCPUs beyond the physical core count per socket increases CPU ready time and co-scheduling overhead, degrading performance instead of improving it.
Detailed technical explanation
How to think about this question
CPU ready time measures the time a VM is ready to run but waiting for a physical CPU; with 8 vCPUs on a host that has 8 cores per socket, the VM requires all cores in a socket to be available simultaneously (co-scheduling), which increases contention when other VMs are active. Storage I/O Control (SIOC) uses a token-based algorithm to throttle I/O from VMs based on shares and limits, ensuring fair access to the NFS datastore and reducing latency during peak load, which is more effective than simply upgrading network bandwidth.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 350-401 question test?
Virtualization — This question tests Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Reduce the number of vCPUs assigned to App-2 from 8 to 4, and configure Storage I/O Control on the datastore. — Option C is correct because App-2's 8 vCPUs exceed the number of physical cores per socket (8), causing CPU scheduling contention and high ready time on App-1, while reducing vCPUs to 4 aligns with the host's core-per-socket count and reduces co-scheduling overhead. Additionally, Storage I/O Control (SIOC) on the NFS datastore can prioritize disk access and mitigate the high disk latency (50 ms) by enforcing shares and limits during congestion, addressing both performance issues without requiring hardware upgrades.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This 350-401 practice question is part of Courseiva's free Cisco 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 350-401 exam.
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